It definitely doesn't seem possible, but this article says 8.9%, and mentions him being the oldest player in the history of MLB to win a game. He played 28 or 29 seasons. When he won, at 49, his catcher was 23.
https://deadspin.com/jamie-moyer-has-faced-8-9-percent-of-all-mlb-hitters-ev-5903536He was undrafted out of high school due to lack of velocity. At 28 and 29, 2 teams/managers gave up on him and one tried to make him a manager. He came back to pitch 20 more years in the majors. At 48, he rehabbed from Tommy John surgery, then pitched the next season at 49. He was on the Mariners team that won the most games in a season in history, and on a Phillies WS Championship team at 45.