Titian and Rembrandt, Monet and Rodin, Frank Lloyd Wright and Le Corbusier, Mark Twain and Henry James, Robert Frost and Elizabeth Bishop, to name a few. Twain wrote 'Tom Sawyer' at 41 and bettered it with 'Huckleberry Finn' at 50; Wright completed Fallingwater at 72 and worked on the Guggenheim Museum until his death at 91.