10. Sandy Koufax
Retirement Age (Career): 30 (1955-1966)
The Left Arm of God left the game on a sour note. The 30-year-old Koufax suffered from an arthritic left elbow that was sometimes black and blue when he woke up in the mornings. Some folks felt he had some more left in the tank because of his phenomenal final year where he went 27-9 with an ERA of 1.73 and 317 Ks. Despite dipping out so early, the Brooklyn-native still helped the Dodgers win four titles and became the first pitcher to win multiple Cy Youngs (two straight upon retiring). Mazel Tov!