The Aging Curve Of MLB Players

We know MLB players peak in their 20s and decline in their 30s. What happens in between? Only millions of tiny changes to their bodies and minds that are nothing short of remarkable.

- Sam Miller

23 There are two outs, the bases are empty and the batter is 23.

He is, as he steps into the batter’s box, the most exciting player in baseball. As a rookie, he has hit a ball 513 feet in batting practice, thrown a pitch 102.5 mph from the mound and reached a top sprint speed—nearly 30 feet per second—faster than three-quarters of his peers can touch. These are the highlight years, and it feels like just the beginning.

But an athlete’s physical decline begins before most of us notice it, and even the 23-year-old body can do things today that it might not be able to do tomorrow. Fastball speed starts going down in a player’s early 20s, and spin rate drops with it. Exit velocity begins to decline at 23 or 24. An average runner slows a little more than 1 inch per second every year, beginning pretty much immediately upon his debut. It takes a little over four seconds for most runners to reach first base, which means with each birthday, it’s as if the bases were pulled 4 inches farther apart. Triples peak in a player’s early 20s, as does batting average on balls put into play. A 23-year-old in the majors is twice as likely to play center field as left field; by 33, the opposite is true.