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Aeschylus 119
ancient Athenian playwright -525–-456 BCRelated quotes

“Epops: A man may learn wisdom even from a foe.”
tr. in Goldstein-Jackson 1983, p. 163 http://books.google.com/books?q=isbn%3A9780389203933+%22A+man+may+learn+wisdom+even+from+a+foe%22+Aristophanes
Birds, line 375-382 (our emphasis on 375 and 378-379 and 382)
Compare the later: "We can learn even from our enemies", Ovid, Metamorphoses, IV, 428.
Birds (414 BC)

“No, that is the great fallacy: the wisdom of old men. They do not grow wise. They grow careful.”
Source: A Farewell to Arms (1929)

“Old men are always young enough to learn.”
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)

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

Go Rin No Sho (1645), The Water Book

"Pythagorean Ethical Sentences From Stobæus" (1904)
Florilegium

The Woodspurge http://www.theotherpages.org/poems/roset03.html#3, st. 4 (1870).