Both age and mileage wear down a fighter, and unfortunately there is no guaranteed formula for determining which one gets them first, or when the rapid decline will happen. Injuries add on to that as well obviously, but I guess that would be part of the "mileage" factor. I would also add that fighters who rely heavily upon their physical tools(reflexes, size, chin, etc.) will be the most noticeable/sudden decline.
So even though you are correct in saying 31 =/= 37, the counter to that is the mileage/toll on the body. Max's chin has eaten a LOT of strikes. And not just volume, often dozens of chin crackers in a single round. His speech is already showing the classic CTE symptoms. He's also mentioned numerous times how much he hates the cut at 145. Even though Volk put on a master clinic in their last match (probably should have been stopped IMO) the things to note were how much more flat footed and slow Max looked. Again, partly that was because of how crazy fast/mobile Volk is, but I think it's at least fair to say that Max isn't in his prime any more. I wouldn't go so far as to say he's shot by any means, just that he's a step down from where he once was. The problem is that he's gonna be tested against the fastest/best in the division due to his ranking, and they are gonna be the ones to expose every step of decline he takes. Will Allen be the one to do it? I'm not sure. But to put it in perspective, if the Yair that just fought Emmett was rematching the Max that just fought Volk I'd put a hefty bet on Yair and I'd probably sprinkle some on a stoppage.
