This is, of course, due to sustained excellence over a set number of years and becoming iconic celebrities whose popularity transcend their sports. Oftentimes in this situation, the athlete is being rewarded with endorsement deals whose cumulative worth far exceed their annual salaries.
There are some athletes, however, who have unquestionably entered the elite plateau in their respective sports early in their careers and are being compensated commensurate with their skill set — or at least what the marketplace will bare, according to bleacherreport.com. And then there is the player or two whose singular God-given attribute is desperately sought after in a particular sports league because of its extreme scarcity (like, for instance, the player above), which drives up the market value of said player. Nobody ever said life was fair.
Take a look at the richest professional athletes age 25 or under.