The average age of UFC HW champions when they won the title is 31.06 years old.
31-33 is prime fighting age.
Only 2 current champions from both UFC and Bellator are under 30 years old, and they're in their late 20s (27 and 28).
The premise that Fedor was old and shopworn at 33 is false. He barely took any damage throughout his career, had no major surgeries, and more than half of his 27 fight unbeaten streak was against unranked fighters, cans, and freakshows. When he fought Werdum, it was the first time in his entire career that he faced 4 top 10 fighters in a row, with Rogers barely making the cut. Fedor would go on to amass a 3-3 (50%) record the first time he fought 6 top 10 guys in a row. Two of them barely made the top 10, and one was ranked in a lower division. The cage, the testing, the competition, and the length of his career all played a part in his eventual downfall. It wasn't just that he was "passed his prime".
Male physical prime starts roughly at 27-28, and begins to decline after 35 in most cases. He's an elite fucking athlete and didn't age faster than most humans.