In addition, there is a vast difference between say tennis, a sport, and chess, a purely mental activity.

A child prodigy in tennis may find that their body didn't grow in such a way to be a pro as an adult. If your opponents are taller, stronger, have better VO2Max, etc. than you as an adult, it doesn't matter how good you were as a child--they're going to beat you as an adult.

Chess, of course, now provides the stark reverse contrast. If you weren't a child prodigy in chess, you simply will not excel against the competition as an adult.