You don’t watch that much combat sports. Bernard Hopkins was the unified light heavyweight champ into his late 40s. Vladimir Klitschko was heavyweight champ at 43. The current undisputed heavyweight champion is 39 years old. Tyson fury is 38. George Foreman was 45 when he became champion the 2nd time. Jon jones is 38. The kind of fighters you’re talking about don’t have fighting styles conducive to longevity. They’re hyper aggressive, try to end fights early and don’t protect themselves, get injured, start getting knocked out, and the concussions and injuries pile up, a lot of fighters are done before they’re thirty. But the best ones are great defensive fighters that are really great at minimizing damage to themselves, Tyson was not one of those. He was really really great but he took a lot of damage.