Meaning

Twain is suggesting that aging is largely a state of mind rather than a fixed physical condition. The wordplay on "mind" and "matter" is the whole engine of the joke: if you genuinely choose not to let the number of your years bother you, then it loses much of its power to define or limit you. The humor is warm rather than dismissive, acknowledging aging as real while arguing that attitude shapes the experience far more than most people allow.

Context

This kind of observation fits naturally into a long tradition of humorous wisdom about growing older, and Twain was a master of that tradition. He wrote and spoke extensively in his later years about life, mortality, and the absurdities of human nature, often using brevity and wordplay to land a point more effectively than a longer argument ever could. The quote's structure, a setup followed by a punning reversal, is a classic example of the aphoristic style he perfected.

About the author

Mark Twain was the pen name of Samuel Langhorne Clemens, born in Missouri in 1835. He is one of the most celebrated figures in American literature, best known for novels including The Adventures of Tom Sawyer and Adventures of Huckleberry Finn. Beyond fiction, he was a prolific essayist, lecturer, and public figure whose commentary on American life and human behavior earned him a devoted following on both sides of the Atlantic. He died in 1910.