Because its snowing out and I have nothing better to do...

Heavyweights:
Oleg Maskaev-40
Evander Holyfield-46
James Toney-40
Matt Skelton-42
Andrew Golota-41
Franois Botha-40

Light Heavyweights:
Bernard Hopkins:44
Antonio Tarver:40
Glen Johnson:40
Roy Jones Jr.:40
Silvio Branco:42

Middleweights:
Javier Castillejo-40
Raymond Joval-40

Super Flyweight:
Pramuansak Posuwam-40 The only fighter below Middleweight to crack the top 50

I have come to the conclusion that old guys can still compete at the top level....but only at light heavyweight