Depends on the individual..some guys are shot in their 20's, some guys like Moore and Nard can be world class fighters into their 40's.
youre too old when youve recently been ko'd by a 10 fight novice, youre 37 and you say things like... "Believe me I am the wonder man, I'll beat them all" ...
there isnt really an age limit as long as your not fighting above where your performance indicates you should be. like if youve been stopped three times in a row then your next fight should not be against an elite level fighter. its back to the club scene for you. for instance people complain about guys like shannan taylor fighting on but i have no problem watching him because hes not chasing world titles against genuine killers anymore.
Frank Ropis just fought a three rounder in Adelaide, watching him train was a treat and by all accounts put on a good show against a 28(?) y.o. The focus on the fight got him into the gym and a target to get fit for, he never got hurt, enjoyed himself and put on a good display. Frank is 57.
IMO depend on the fighter. A reflex guy like RJJ should be early-mid 30s. Whereas a well schooled boxer like Hopkins can go to 40. Boxing can be a bit of a contradiction I reckon. The more time someone has in sparring and fights the better they get - experience, even after 20 years guys are still getting better. But the trade off is they physically decline.
how long is a piece of string? depends on the style... guy like RJJ that relies on speed, needs to retire at 35 maximum guy like Katsidis who is an all out brawler? 30 i reckon Old school fighter like B-Hop or Toney? They can go until they get totally schooled A balanced fighter like Holyfield with speed, power and chin? Now