This would be slightly on-topic if I were listing the children's writers as well - but that part will have to wait for at least a day or two. I have too much work to deal with, plus friends and family to see!

Unless there's a fantasy or SF writer here I overlooked...

Writers for adults (many can be seen at genarians.com):

1915 Ma Shitu (Chinese politician/novelist)

1916 Geneviève Callerot (French novelist)

1917 Lise Nørgaard (Danish journalist/writer)

1918 Naomi Replansky (American poet), Doris Grumbach (American novelist/biographer/critic)

1920 Ted Knap (American journalist)

1921 Hossein Wahid Khorasani (Iranian religious writer), Hans Albert (German philosopher), Ray Lawler (Australian playwright), Edgar Morin (French philosopher)

1922 Bernard Kalb, Bernard Weisberger, William Leuchtenburg, Angel Wagenstein, Jean Malaurie

1923 Edward Lueders, Ida Vitale, Józef Hen

1924 Richard Rohmer, David Ferry, Herbert Gold, Edward Field, Guadalupe Rivera Marin

1925 Eugen Gomringer, Gerald Stern, Alain Touraine, Madeleine Chapsal

1926 Jürgen Moltmann, Ruth Minsky Sender, Arno J. Mayer, Frederick Buechner, Sami Michael, Rene Depestre

1927: Martin Walser, Nayantara Sahgal, David Ireland, Carlos Germán Belli, James Roose-Evans, Willis Barnstone

1928: Daisaku Ikeda, William Kennedy, Desmond Morris, E.D. Hirsch, Tom Lehrer, Cynthia Ozick, Howard S. Becker, Michelle Perrot, Dr. Ruth Westheimer, Patrick Hemingway, Griselda Gambaro, Pavel Kohout, Jayanta Mahapatra, Christopher Davis, Noam Chomsky

1929: Amitai Etzioni, Peter Dale Scott, Alasdair MacIntyre, Len Deighton, Milan Kundera, Antonine Maillet, Harvey Cox, Harry Frankfurt, Jurgen Habermas , Arthur Frommer, Emmanuel Le Roy Ladurie, X.J. Kennedy, Dr. Robert Coles, Hans M. Enzensberger

1930: Adonis, Jennifer Johnston, Norman Podhoretz, Luce Irigaray, Gary Snyder, John Barth, Thomas Sowell, Selma James, Johan Galtung, Stuart Briscoe, Kenneth Frampton, Christopher Nicole, Dame Edna O'Brien

1931: John McPhee, John Norman, Jorge Edwards, Alice Munro, Ivan Klima, Adrienne Kennedy, Fay Weldon, Charles Taylor, Jerome Rothenberg

1932: Robert Coover, Gay Talese, Andrew Young, John Jakes, Elena Poniatowska, Paul R. Ehrlich, Athol Fugard, Stephen Gill

On Sunday, July 3, 2022 at 2:41:22 PM UTC-4, Lenona wrote:
[snip-snip]
> 1920 Ted Knap (American journalist)

Bob Madle, who turned 102 last month, is primarily a dealer, a fan
and a reviewer, but he *has* published a few SF stories -- see
http://www.isfdb.org/cgi-bin/ea.cgi?24461

Here are most of the living juvenile writers, some of whom write SF and fantasy:

https://groups.google.com/g/alt.obituaries/c/oPTFMY3aPfI

Note the question at the end about the British SF writer Lois Lamplugh.

On Friday, July 8, 2022 at 3:26:40 PM UTC-4, Lenona wrote:
> Here are most of the living juvenile writers, some of whom write SF and fantasy:
>
> https://groups.google.com/g/alt.obituaries/c/oPTFMY3aPfI
>
> Note the question at the end about the British SF writer Lois Lamplugh.

I am afraid our (ISFDB) knowledge is limited to what her author record
says in our database.

In article <74339ae2-912c-4c84-ad5f-289976c3bac7n@googlegroups.com>,
Ahasuerus <ahasuerus@email.com> wrote:
>On Friday, July 8, 2022 at 3:26:40 PM UTC-4, Lenona wrote:
>> Here are most of the living juvenile writers, some of whom write SF
>and fantasy:
>>
>> https://groups.google.com/g/alt.obituaries/c/oPTFMY3aPfI
>>
>> Note the question at the end about the British SF writer Lois Lamplugh.
>
>I am afraid our (ISFDB) knowledge is limited to what her author record
>says in our database.

I would say about the oldest a juvenile writer can be is 16.
--
columbiaclosings.com
What's not in Columbia anymore..

On Friday, July 8, 2022 at 5:35:35 PM UTC-4, Ted Nolan <tednolan> wrote:
> In article <74339ae2-912c-4c84...@googlegroups.com>,
> Ahasuerus <ahas...@email.com> wrote:
> >On Friday, July 8, 2022 at 3:26:40 PM UTC-4, Lenona wrote:
> >> Here are most of the living juvenile writers, some of whom write SF
> >and fantasy:
> >>
> >> https://groups.google.com/g/alt.obituaries/c/oPTFMY3aPfI
> >>
> >> Note the question at the end about the British SF writer Lois Lamplugh.
> >
> >I am afraid our (ISFDB) knowledge is limited to what her author record
> >says in our database.
> I would say about the oldest a juvenile writer can be is 16.

Not according to
https://www.justice.gov/archives/jm/criminal-resource-manual-38-juvenile-defined
!

And:

1932
Brenda R. Lewis (British nonfiction writer: "The Story of Anne Frank," 2001)
Arielle North Olson ("Ask the Bones: Scary Stories from Around the World," 1999 - daughter of Sterling North)
Jo Harper ("Prairie Dog Pioneers," 1998)
Irene Bennett Brown (YA novelist: "Before the Lark," 1982)
Adjai Robinson (Sierra Leonean writer: "Singing Tales of Africa," 1974)
Marjorie Stapleton (British writer: "Make Things Gypsies Made," 1974)
Marian Hostetler (Mennonite writer: "African Adventure," 1978)
C.S. Adler ("Good-Bye Pink Pig," 1986)
Josef Palecek (Czech fairy-tale illustrator/filmmaker)
Mary Small (British-born Australian writer: "Tracey McBean & the Stretching Machine," 1989)
Mary Ray (British novelist: "Roman Empire" series)
Norman Richards (biographer/history writer)
Linell Nash Smith (writer/illustrator: "Custard the Dragon," by Ogden Nash)
Eileen Deacon (British 1970s crafts writer)
Johanna Reiss (Dutch-born writer & 1973 Newbery Honoree: "The Upstairs Room")
Joan Lingard (Scottish writer: "Sadie & Kevin" series, 1970s)
Angelo Torres (MAD cartoonist)
Debby Slier (South African-born writer: "Hello Kitty" series, 1980s)
Sylvia Sherry (British writer: "Rocky O'Rourke" series, 1969-1992)
Aino Pervik (Estonian author & 2014 HCAA nominee)
Bryna J. Fireside (nonfiction writer: "Is There a Woman in the House...or Senate?" 2000)
Nonny Hogrogian (Caldecott Medalist: 1966 & 1972)
Lorenzo Lynch (illustrator: Arnold Adoff's "Big Sister Tells Me I'm Black," 1976)
Jill Chaney (British YA novelist: "Mottram Park" series, 1971-1989)
Lois Simmie (Canadian poet: "An Armadillo Is Not a Pillow," 1986)
Spiridon Vangheli (Moldovan poet/novelist and 1998 HCAA nominee)
Joe Servello (illustrator & Caldecott nominee: 1972 & 1973)
Phyllis Green ("Eating Ice Cream With a Werewolf," 1983)
Gwendolyn E. Reed (compiler: "Out of the Ark: An Anthology of Animal Verse," 1968)
Russell E. Erickson ("A Toad for Tuesday," 1998)

On 7/8/2022 4:35 PM, Ted Nolan <tednolan> wrote:
> In article <74339ae2-912c-4c84-ad5f-289976c3bac7n@googlegroups.com>,
> Ahasuerus <ahasuerus@email.com> wrote:
>> On Friday, July 8, 2022 at 3:26:40 PM UTC-4, Lenona wrote:
>>> Here are most of the living juvenile writers, some of whom write SF
>> and fantasy:
>>>
>>> https://groups.google.com/g/alt.obituaries/c/oPTFMY3aPfI
>>>
>>> Note the question at the end about the British SF writer Lois Lamplugh.
>>
>> I am afraid our (ISFDB) knowledge is limited to what her author record
>> says in our database.
>
> I would say about the oldest a juvenile writer can be is 16.

Robert Heinlein wrote juvenile SF into his 40s.

I just read a juvenile SF book by a guy in at least his 30s.
https://www.amazon.com/gp/product/0062306723

And Will McIntosh wrote "Watchdog" in his 50s about a pair of 13 year
old twins who built a robot dog.
https://www.amazon.com/gp/product/B01NAW3JZ9/

Lynn

On Friday, 8 July 2022 at 22:35:35 UTC+1, Ted Nolan <tednolan> wrote:
> In article <74339ae2-912c-4c84...@googlegroups.com>,
> Ahasuerus <ahas...@email.com> wrote:
> >On Friday, July 8, 2022 at 3:26:40 PM UTC-4, Lenona wrote:
> >> Here are most of the living juvenile writers, some of whom write SF
> >and fantasy:
> >>
> >> https://groups.google.com/g/alt.obituaries/c/oPTFMY3aPfI
> >>
> >> Note the question at the end about the British SF writer Lois Lamplugh.
> >
> >I am afraid our (ISFDB) knowledge is limited to what her author record
> >says in our database.
> I would say about the oldest a juvenile writer can be is 16.

I'd draw the line at 18. But stuck in my memory
is a recurring British 1960s radio parody in show
_Round the Horne_ (starring Kenneth Horne) of
1930s-40s movie romance scenes, always featuring
"Charles" and "Fiona" played by "Dame Celia Molestrangler"
and "ageing juvenile Binkie Huckaback", all fictional.

"Juvenile lead" basically means acting in the romantic
hero role, but not necessarily as a teenager, and Charles
and Fiona clearly have a lot of history, not only with
each other.

On 12/07/2022 21.28, Robert Carnegie wrote:
> On Friday, 8 July 2022 at 22:35:35 UTC+1, Ted Nolan <tednolan> wrote:
>> In article <74339ae2-912c-4c84...@googlegroups.com>,
>> Ahasuerus <ahas...@email.com> wrote:
>>> On Friday, July 8, 2022 at 3:26:40 PM UTC-4, Lenona wrote:
>>>> Here are most of the living juvenile writers, some of whom write SF
>>> and fantasy:
>>>>
>>>> https://groups.google.com/g/alt.obituaries/c/oPTFMY3aPfI
>>>>
>>>> Note the question at the end about the British SF writer Lois Lamplugh.
>>>
>>> I am afraid our (ISFDB) knowledge is limited to what her author record
>>> says in our database.
>> I would say about the oldest a juvenile writer can be is 16.
>
> I'd draw the line at 18. But stuck in my memory
> is a recurring British 1960s radio parody in show
> _Round the Horne_ (starring Kenneth Horne) of
> 1930s-40s movie romance scenes, always featuring
> "Charles" and "Fiona" played by "Dame Celia Molestrangler"
> and "ageing juvenile Binkie Huckaback", all fictional.
>
> "Juvenile lead" basically means acting in the romantic
> hero role, but not necessarily as a teenager, and Charles
> and Fiona clearly have a lot of history, not only with
> each other.

In _Gold Diggers of 1933_, the (internal) show's juvenile lead
says that he's been a juvenile for 18 years, and knows his job.
"Brad" (played by Dick Powell) later takes his place. Powell
himself played juveniles into his 40s (per IMDB).

--
Michael F. Stemper
The name of the story is "A Sound of Thunder".
It was written by Ray Bradbury. You're welcome.

On Tue, 12 Jul 2022 17:16:01 -0500, Lynn McGuire
<lynnmcguire5@gmail.com> wrote:

>On 7/8/2022 4:35 PM, Ted Nolan <tednolan> wrote:
>> In article <74339ae2-912c-4c84-ad5f-289976c3bac7n@googlegroups.com>,
>> Ahasuerus <ahasuerus@email.com> wrote:
>>> On Friday, July 8, 2022 at 3:26:40 PM UTC-4, Lenona wrote:
>>>> Here are most of the living juvenile writers, some of whom write SF
>>> and fantasy:
>>>>
>>>> https://groups.google.com/g/alt.obituaries/c/oPTFMY3aPfI
>>>>
>>>> Note the question at the end about the British SF writer Lois Lamplugh.
>>>
>>> I am afraid our (ISFDB) knowledge is limited to what her author record
>>> says in our database.
>>
>> I would say about the oldest a juvenile writer can be is 16.
>
>Robert Heinlein wrote juvenile SF into his 40s.
>
>I just read a juvenile SF book by a guy in at least his 30s.
> https://www.amazon.com/gp/product/0062306723
>
>And Will McIntosh wrote "Watchdog" in his 50s about a pair of 13 year
>old twins who built a robot dog.
> https://www.amazon.com/gp/product/B01NAW3JZ9/

You do realize that this is based on an ambiguous use of "juvenile
writer", right?
--
"In this connexion, unquestionably the most significant
development was the disintegration, under Christian
influence, of classical conceptions of the family and
of family right."

On 7/13/2022 11:27 AM, Paul S Person wrote:
> On Tue, 12 Jul 2022 17:16:01 -0500, Lynn McGuire
> <lynnmcguire5@gmail.com> wrote:
>
>> On 7/8/2022 4:35 PM, Ted Nolan <tednolan> wrote:
>>> In article <74339ae2-912c-4c84-ad5f-289976c3bac7n@googlegroups.com>,
>>> Ahasuerus <ahasuerus@email.com> wrote:
>>>> On Friday, July 8, 2022 at 3:26:40 PM UTC-4, Lenona wrote:
>>>>> Here are most of the living juvenile writers, some of whom write SF
>>>> and fantasy:
>>>>>
>>>>> https://groups.google.com/g/alt.obituaries/c/oPTFMY3aPfI
>>>>>
>>>>> Note the question at the end about the British SF writer Lois Lamplugh.
>>>>
>>>> I am afraid our (ISFDB) knowledge is limited to what her author record
>>>> says in our database.
>>>
>>> I would say about the oldest a juvenile writer can be is 16.
>>
>> Robert Heinlein wrote juvenile SF into his 40s.
>>
>> I just read a juvenile SF book by a guy in at least his 30s.
>> https://www.amazon.com/gp/product/0062306723
>>
>> And Will McIntosh wrote "Watchdog" in his 50s about a pair of 13 year
>> old twins who built a robot dog.
>> https://www.amazon.com/gp/product/B01NAW3JZ9/
>
> You do realize that this is based on an ambiguous use of "juvenile
> writer", right?

Nope.

Lynn

On Wednesday, 13 July 2022 at 18:53:19 UTC+1, Lynn McGuire wrote:
> On 7/13/2022 11:27 AM, Paul S Person wrote:
> > On Tue, 12 Jul 2022 17:16:01 -0500, Lynn McGuire
> > <lynnmc...@gmail.com> wrote:
> >
> >> On 7/8/2022 4:35 PM, Ted Nolan <tednolan> wrote:
> >>> In article <74339ae2-912c-4c84...@googlegroups.com>,
> >>> Ahasuerus <ahas...@email.com> wrote:
> >>>> On Friday, July 8, 2022 at 3:26:40 PM UTC-4, Lenona wrote:
> >>>>> Here are most of the living juvenile writers, some of whom write SF
> >>>> and fantasy:
> >>>>>
> >>>>> https://groups.google.com/g/alt.obituaries/c/oPTFMY3aPfI
> >>>>>
> >>>>> Note the question at the end about the British SF writer Lois Lamplugh.
> >>>>
> >>>> I am afraid our (ISFDB) knowledge is limited to what her author record
> >>>> says in our database.
> >>>
> >>> I would say about the oldest a juvenile writer can be is 16.
> >>
> >> Robert Heinlein wrote juvenile SF into his 40s.
> >>
> >> I just read a juvenile SF book by a guy in at least his 30s.
> >> https://www.amazon.com/gp/product/0062306723
> >>
> >> And Will McIntosh wrote "Watchdog" in his 50s about a pair of 13 year
> >> old twins who built a robot dog.
> >> https://www.amazon.com/gp/product/B01NAW3JZ9/
> >
> > You do realize that this is based on an ambiguous use of "juvenile
> > writer", right?
> Nope.

A writer of juvenilia and we'd better look up what that is....
Dictionary.com thinks it /can/ mean literary or artistic
productions for a young audience. I think that's incorrect.
But it seems to be how Leonora meant it.

On Wed, 13 Jul 2022 15:37:18 -0700 (PDT), Robert Carnegie
<rja.carnegie@excite.com> wrote:

>On Wednesday, 13 July 2022 at 18:53:19 UTC+1, Lynn McGuire wrote:
>> On 7/13/2022 11:27 AM, Paul S Person wrote:
>> > On Tue, 12 Jul 2022 17:16:01 -0500, Lynn McGuire
>> > <lynnmc...@gmail.com> wrote:
>> >
>> >> On 7/8/2022 4:35 PM, Ted Nolan <tednolan> wrote:
>> >>> In article <74339ae2-912c-4c84...@googlegroups.com>,
>> >>> Ahasuerus <ahas...@email.com> wrote:
>> >>>> On Friday, July 8, 2022 at 3:26:40 PM UTC-4, Lenona wrote:
>> >>>>> Here are most of the living juvenile writers, some of whom write SF
>> >>>> and fantasy:
>> >>>>>
>> >>>>> https://groups.google.com/g/alt.obituaries/c/oPTFMY3aPfI
>> >>>>>
>> >>>>> Note the question at the end about the British SF writer Lois Lamplugh.
>> >>>>
>> >>>> I am afraid our (ISFDB) knowledge is limited to what her author record
>> >>>> says in our database.
>> >>>
>> >>> I would say about the oldest a juvenile writer can be is 16.
>> >>
>> >> Robert Heinlein wrote juvenile SF into his 40s.
>> >>
>> >> I just read a juvenile SF book by a guy in at least his 30s.
>> >> https://www.amazon.com/gp/product/0062306723
>> >>
>> >> And Will McIntosh wrote "Watchdog" in his 50s about a pair of 13 year
>> >> old twins who built a robot dog.
>> >> https://www.amazon.com/gp/product/B01NAW3JZ9/
>> >
>> > You do realize that this is based on an ambiguous use of "juvenile
>> > writer", right?
>> Nope.
>
>A writer of juvenilia and we'd better look up what that is....
>Dictionary.com thinks it /can/ mean literary or artistic
>productions for a young audience. I think that's incorrect.
>But it seems to be how Leonora meant it.

I'm putting this here to acknowledge your research.

The two meanings apparently being used here seem to me to be:

1) A writer of books aimed at young people. The writers are generally
not young persons at the time they write the books.

2) A writer of books who /is/ a young person. And, no, they don't have
to be writing books for young persons.

There are, of course, several age ranges for "young person", ranging
from Very Young Indeed (Mother Goose etc) to teenagers.

The best definition of "juvenile book" (for teenagers) I have ever
encountered (probably in this newsgroup) was "any book a teenager will
voluntarily purchase and read". As opposed to school assignments.
--
"In this connexion, unquestionably the most significant
development was the disintegration, under Christian
influence, of classical conceptions of the family and
of family right."