Always with one more story to tell-

P.G. Wodehouse in his last years. He died in 1975 at 93.

From an article on authors active in their 80s:

In his posthumous collection of essays, On Late Style: Music and Literature Against the Grain, Edward Said contended that late-life work isn’t always a summing up, or a display of accumulated wisdom, or a reassessment; it can also be “a form of exile” marked by “intransigence, difficulty and unresolved contradiction.” 

Said cited Jean Genet and Ludwig von Beethoven, among others, as exemplars of this intransigence. Late style can also be a response to the breakdown of the body, as when Henri Matisse underwent colon surgery at age 71 and, no longer able to stand and work at an easel, gleefully embarked on what he called his “second life,” a 13-year flurry when he sat in a wheelchair and used simple scissors and sheets of colored paper to create the ebullient, child-like cutouts that would become the exclamation point of his long career. He kept at it until he suffered a fatal heart attack at the age of 84. 

The painter Chuck Close, who underwent a major stylistic shift of his own in his mid-70s, recently said, “The late stage can be very interesting. Had Matisse not done the cutouts, we would not know who he was.” 

The above list doesn’t pretend to be exhaustive. It omits countless octogenarians who are still doing fine work, as well as writers who were productive until they died in their 80s (and beyond), including: Maya Angelou, who died at 86 in 2014; the poet John Ashbery, still prolific at 89; Saul Bellow, who died at 89 in 2005; E.L. Doctorow, who died last year at 84 and will posthumously publish his Collected Stories next year; Elizabeth Hardwick, who died at 91 in 2007; Gabriel García Márquez, who died at 87 in 2014; the Canadian short story master and Nobel laureate, Alice Munro, still working at 85; Philip Roth, (who is currently in retirement but was productive into his 80s); James Salter, who died last year at 90; and Tom Wolfe (85). 

As different as these writers are, they do have one thing in common: they were all in for the long haul, and they all found a way to keep up the good work.