Muhammad Ali lost to Trevor Berbick at 39 Mike Tyson lost to Kevin McBride at 39 Lennox Lewis refused a rematch and retired at 37 after getting dominated in his fight While... Vitali Klitschko dominated the #1 HW contender at 40 years old.
What was bitchko at 20 the age Tyson won the HW - Let me guess, still trying to learn how to shadow box!
Your comparison doesn't work. Berbick is a a former WBC world champion, while Chisora is 17 fight novice with ZERO amateur experience. As for Tyson, the guy wasn't even six foot, so he relied on lightning fast reflexes and hand speed to close the gap. Once that was lost by age and bad lifestyle choices he had very little left. Vitali, on the other hand, has the advantage of outweighing and towering over every opponent he faces and most of them are pretty **** anyway.
