How is a 38 year old man who heavily relies on movement still dominating?

People are living longer and longer and as a result are comparatively younger at any given age than previously.

 

Usyk is a great, great heavyweight, that goes without saying, but let's not fall for the misconception that he has been 'much older' than his opposition. Usyk's heavyweight opponents have been :

Witherspoon - 6 years older than Usyk.
Chisora - 4 years older than Usyk.
Joshua - 2 years younger than Usyk.
Fury - less than 2 years younger than Usyk.
Dubois - 10 years younger than Usyk.

The vast majority of these guys are older or similarly aged to Usyk - Dubois being the exception - and nearly every one of them is a plodder, not in any way renowned for their fancy footwork.