“Young men, hear an old man to whom old men hearkened when he was young.”

Act V, scene i.
All Fools (1605)

Source: Letters, p. 250

Quoted in Colin Jarman's The Guinness Dictionary of Sports Quotations (1990)

Comparing Richard Nixon to Alben Barkley during the 1952 presidential race, as quoted in Richard Nixon: A Political and Personal Portrait (1959) by Earl Mazo, Chapter 7

Eleven Declarations of War (London: Harcourt Brace, 1975) p. 11

Jacula Prudentum (1651)

Variant translation: Learning is ever in the freshness of its youth, even for the old.
Source: Oresteia (458 BC), Agamemnon, line 584 ( line 583 of Richmond Lattimore's translation http://books.google.com/books?id=3duN7nP3OQYC&q=%22old+men+are+always+young+enough+to+learn%22&pg=PA40#v=onepage)

Of Marriage and Single Life
Essays (1625)