Maybe Fenris can help me out, but I remember a quote by Bob Heinlein, where he’s telling a story about how someone said to him that there are no retired writers. There are retired postmen, doctors, engineers, lawyers, but not writers. The conclusion is that people who write for a living don’t do it because they want the money or fame or attention. They do it because they have to. They simply can’t stop.
Which explains Stephen King.
There are a million writers who retired because they wanted to, a million writers who retired because they no longer had anything to say, a million writers who retired because they couldn’t sell any more, a million writers who retired because of ill health, a million… You get the point.
I won’t go so far as to say that any aphorism of Heinlein’s is sure to apply to him and only coincidentally to the rest of the world, but it’s a good first approximation.
Anyway, baseball writer Roger Angell is over 80. There was just an article in Writer magazine by Hervie Haufler, who’s 85 and just had a book he wrote in retirement published. Nelson Bond, a science fiction writer as old as Jack Williamson, started writing again after he was named Author Emeritus by SFWA and reunited with his sf friends, including Williamson. Jacques Barzun, the noted scholar, published From Dawn to Decadence in 2001 at the age of 94 and I believe he’s still around and working. Gore Vidal will be 80 this year and so will his nemesis William F. Buckley. Carl Reiner, who has written a number of books in addition to all those movies and tv shows, the most recent in 2003, will be 83. Madeleine L’Engle is 86.
They’re both dead now, but Bessie & Sadie Delany were both well over 100 when their memoirs, Having Our Say, was published. (I don’t know how much of the actual writing they did, but a sequel, On My Own at 107, was published by Sadie when she was actually 108 (she lived to be 110).
At 74 he’s a few years too young to be on your list, but I’ll mention him anyway: Tom Wolfe is the author of one of the bestselling books in the country at the moment and it’s written from the perspective of a teenaged 21st century girl.
Jorge Luis Borges was productive as a writer and lecturer at the time of his death even though he was almost 87 and had been totally blind for decades.
P.G. Wodehouse lived to the age of 94 and was writing Jeeves and Wooster stories practically to the end.
And, as I think I proved fairly well here, Jeeves and Wooster seem to have the distinction of being the fictional characters written about by the original author over the longest period: 58 years, from 1916 to 1974. (Wodehouse died in early '75.)