“Youth is a circumstance you can't do anything about. The trick is to grow up without getting old.”

Source: Attributed to Parker after her death, by Robert E. Drennan The Algonquin Wits (1968), p. 124. However the same quip appears anonymously fifteen years earlier, in the trade journal Sales Management (Chicago: Dartnell Corp., 1918-75), vol. 70 (Survey of Buying Power, 1953), p. 80: "Marxism never changes. You can’t teach an old dogma new tricks."

Source: To Kill a Mockingbird

Variant: I wish you would tell me your secret. To get back my youth I would do anything in the world, except take exercise, get up early, or be respectable.
Source: The Picture of Dorian Gray

Source: Dictionary of Burning Words of Brilliant Writers (1895), P. 439.

Address at the National Plowing Match (18 September 1948); as quoted in Miracle of '48: Harry Truman's Major Campaign Speeches and Selected Whistle-stops (2003); edited by Steve Neal. Truman's mention of an "old political trick" is often quoted alone as if it were a strategy he was advising rather than one he was criticizing.
Context: On the one hand, the Republicans are telling industrial workers that the high cost of food in the cities is due to this government's farm policy. On the other hand, the Republicans are telling the farmers that the high cost of manufactured goods on the farm is due to this government's labor policy.
That's plain hokum. It's an old political trick: "If you can't convince 'em, confuse 'em." But this time it won't work.

Vivie, Act II
Source: 1890s, Mrs. Warren's Profession (1893)

Source: This is Where I Leave You