I'm trying to think of other demanding sports, compare it to football for example. The worlds best players are mostly all under 25 (Rooney, Messi, Ronaldo) there are many others who ripen with age, but the very best are normally the younger guys.

Take a look through the pound for pound in each weight class and you'll see the top in each weight is over 30. All but the smallest, this is probably while fighters still grow.

It must be something to do not only with the knowledge, but how your body develops. Using say Khan as an example, your a man at 18, but his physical shape is completley different now than a few years ago and we expect him to get bigger and stronger with age.

I think your right though, punchers get wear and tear quicker, mainly due to their intent on slugging it out. The cumulative effect of punches takes effect later on.

How the hell did the old dogs do 150 fights? Especially seeing some if not most were 15+ rounds.

Which asks another question, will anyone ever come close or be able to repeat those feats? Given that we all would agree modern boxers are fitter and better conditioned. None of this fight every 6 month bollocks!