So whats wrong with training, sparring or fighting with people your own age?

Dont look for an excuse. Brockton will find like minded souls of his own age at white collar level at least. If his skill level is good enough after a period of training, he will also find some bum journeymen/novices he can compete with at pro level. He also wouldnt get a licence to fight pro unless he is deemed fit to fight anyway.