An enthusiastic tennis player, Supreme Court Justice Hugo Black was dismayed one day to have his doctor tell him that the sport was inadvisable for someone in his forties. "In that case," Black replied, "I can't wait to turn fifty so I can play again."
Sources
The Friars Club Encyclopaedia of Jokes: 2,000 One-Liners, Straight Lines, Stories, Gags, Roasts, Ribs and Put-Downs