Charles Dickens, "The Black Veil" (1836):
They do say, that as life steals on towards its final close, the last short remnant, worthless as it may seem to all beside, is dearer to its possessor than all the years that have gone before, connected though they be with the recollection of old friends long since dead.
As an attractive woman passed by, former French PM Georges Clemenceau on his 80th birthday in 1921, he said to a friend: "Oh, to be seventy again." (He lived to 88)
F. Scott Fitzgerald, "O Russet Witch!" from Tales of the Jazz Age (1922)
The years between thirty-five and sixty-five revolve before the passive mind as one unexplained, confusing merry-go-round. ... For most men and women these thirty years are taken up with a gradual withdrawal from life, a retreat first from a front with many shelters, those myriad amusements and curiosities of youth, to a line with less, when we peel down our ambitions to one ambition, our recreations to one recreation, our friends to a few ... ; ending up at last in a solitary, desolate strong point that is not strong, where the shells now whistle abominably, now are but half-heard as, by turns frightened and tired, we sit waiting for death.
W. Somerset Maugham, "Cakes and Ale" (1930):
A man who is a politician at forty is a statesman at three score and ten. It is at this age, when he would be too old to be a clerk or a gardener or a police-court magistrate, that he is ripe to govern a country. This is not so strange when you reflect that from the earliest times the old have rubbed it into the young that they are wiser than they, and before the young had discovered what nonsense this was they were old too, and it profited them to carry on the imposture; and besides, no one can have moved in the society of politicians without discovering that (if one may judge by results) it requires little mental ability to rule a nation.
W. Somerset Maugham, "The Lotus Eater" (1935):
"I knew pretty well how much [money] I needed. I found I had just enough to buy an annuity for twenty-five years."
"You were thirty-five at the time?"
"Yes. It would carry me on till I was sixty. After all, no one can be certain of living longer than that, a lot of men die in their fifties, and by the time a man's sixty he's had the best of life."
Gene D. Cohen, The Creative Age: Awakening Human Potential in the Second Half of Life (2000), p. 47.
[The] simple contrast in the way cells age is one of the most fundamental differences between the aging brain and the aging body, even though they are obviously part of the same organism: They differ in their potential for ultimate accomplishment with age. When we compare outstanding performance of different age groups, we can see differences in physical and mental performance.
Somebody at age seventy may be in great physical shape for his age, and may be a great runner in his age group, but would not be able to compete with an outstanding young runner who was twenty-five. Yet the same cannot be said in comparing intellectual performance. A seventy-year-old historian, for example, could very well run circles around a twenty-five-year-old Rhodes history scholar when it comes to discussing or interpreting history.
I have added my own thoughts on aging: "At 75, Staying Healthy Is My New Career" (2024).