“No, that is the great fallacy: the wisdom of old men. They do not grow wise. They grow careful.”

Source: A Lodge in the Wilderness (1906), Ch. XI, pp. 313–4

Les hommes vieillissent, mais ne mûrissent pas.
Source: Notes sur la vie (published posthumously 1899), P. 103; translation p. 380.

Lexicon Tetraglotton (1660)

Source: Works and Days (c. 700 BC), line 93.

Source: The Godfather

This is an anonymous modern quip which is a variant of a statement by G. Stanley Hall, in Adolescence: Its Psychology and Its Relations to Physiology, Anthropology, Sociology, Sex, Crime, Religion and Education (1904):
: Men grow old because they stop playing, and not conversely.
Misattributed

Source: Antigone, Line 1347, closing lines

"To the Indianapolis Clergy." The Iconoclast (Indianapolis, IN) (1883)
Context: The inventor of paper—and he was not a Christian—did more than all the early fathers for mankind. The inventors of plows, of sickles, of cradles, of reapers; the inventors of wagons, coaches, locomotives; the inventors of skiffs, sail-vessels, steamships; the men who have made looms—in short, the inventors of all useful things—they are the civilizers taken in connection with the great thinkers, the poets, the musicians, the actors, the painters, the sculptors. The men who have invented the useful, and the men who have made the useful beautiful, are the real civilizers of mankind. The priests, in all ages, have been hindrances—stumbling-blocks. They have prevented man from using his reason. They have told ghost stories to courage until courage became fear. They have done all in their power to keep men from growing intellectually, to keep the world in a state of childhood, that they themselves might be deemed great and good and wise. They have always known that their reputation for wisdom depended upon the ignorance of the people.

The Waiting Song
Song lyrics