For the record, just because your past your prime doesn't mean your not world class. Instead of "past your prime" the proper worded should be "past your peak" because the former is so derogatory as far as explaining where a fighter is at their careers. Examples of past peak fighters still putting on great performances
Bernard Hopkins vs Antonio Tarver, Kelly Pavlik, Winky Wright (snoosefest but still great considering his age), Joe Calzaghe, Both Jermain Taylor fights.
Lennox Lewis vs David Tua, Hasim Rahman II, and Michael Grant
Vitali Klistchko vs Sam Peter, Chris Arreola and soon to be David Haye
Glen Johnson vs Chad Dawson I, Roy Jones fight, and to an extent Antonio Tarver fight.
Pongsaklek Wonjongkam vs Koki Kameda
I mean I can go on, but you guys get the point. Also I only used recent examples and if I dug into the history of the sport, this list would never end.