Ronald Reagan was in his fifties when he started his real career as a politican. Vince Lombardi was 45 when he took the head coaching job with the Green Bay Packers. George Patton was 60 when he took over command of the 2nd Armored Division, and all of his noted work came after that. Teddy Roosevelt, the youngest man ever to hold the office of President, was 43 when he took office. Michelangelo was about forty when he did his celebrated sculpture of Moses, and continued working until his death when he was 89. Leonardo da Vinci was in his forties when he did the Last Supper and his fifties when he completed the Mona Lisa. Claude Monet was in his sixties when he did his "Water Lilies" paintings. Neil Armstrong was 16 days from his 40th birthday when he stepped on the moon (born on August 5, 1930, stepped on moon July 20, 1969).
There are a zillion more examples.