For the longest time people thought that a baseball player's prime was like, ages 27-29, and then people actually studied it and found that actually no, most players primes were actually far, far earlier. Like, early 20s to mid-20s (if that). There are freaks of nature out there but they are the exception, not the rule.
It's far worse with football players. Most of the value of a given player will be on their first contract, when drafted.