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No mathematician should... allow himself to forget that mathematics, more than any other art or science, is a young man's game. ...Newton gave up mathematics at fifty; ...by the time he was forty ...his great creative days were over. His greatest ideas.., fluxions and the law of gravitation, came... about 1666, when he was twenty four... He made big discoveries until... nearly forty (the 'elliptic orbit' at thirty-seven), but after that he did little but polish and perfect.
— G. H. HARDY