Koufax hadn't lost any velocity. He retired because he was diagnosed with an arthritic condition in his elbow. He acknowledged that he could still pitch, but he retired, because he was uncertain how the condition would affect him later in life. Long story short, when he retired the arthritic condition disappeared. I heard stories that well into his 50's he was still bringing the ball in the 80's at Dodgers ST. The arthritic condition was no doubt from overuse. He pitched a complete game victory in game 7 of the 65 WS on two days rest. He usually worked on 3 days rest. Today, he would be a pampered multi-million property and he would have pitched much longer. Pedro has the advantage of advances in training, sports medicine etc. He'll be effective for some time to come, maybe even after his contract expires, if he wants to keep pitching.