Hello all :
That was the best answer I have heard yet ! I would like to add to this. In my years in the fight game, I have ran into this question many of times, and another question that goes hand in hand is peoples perception of peaking, due to age. A fighter peaks after years in the boxing game, reaching the peak has nothing to do with age....However, physical strength and endurance, stamina, these things are related to age. Let me put it this way.
When I get a young fighter in my gym, 11-12 years old, I have them train 3 times a week, and I do not get mad when they miss training. When I get a 16-28 year old that is very serious about fighting, I have them train 5 days a week, with Saturday being optional. The older group will run everyday, 7 days a week. This training regimen is very hard. Boxing is a life style, a discipline, and it takes dedication. So to me the peak will come at about 4 years of training like this, then the crafty old gym workhorse will emerge, you know the guy that can go 100 rounds sparring and never tire, lol. But his decline is in his/hers strength and endurance and stamina.....what do you all think?