Jeff Zimmerman of Fangraphs recently wrote an article examining how the accumulation of injuries in a career prematurely ages pitchers versus those pitchers that are better able to avoid injury. In conducting his research, Zimmerman only looked at starting pitchers, and he looked at injury accumulation from 2010-2018. He divided those pitchers that qualified under these criteria by steep production decline starting at age 29.
The steep production decline starting at age 29 for starting pitchers (and hitters for that matter) as a group has been born out by Zimmerman’s work in the Hardball Times.