trying to think of fighters who fought at world title level or world title contender level over the age of 40... sure i can't think of most of them...be interesting to have a list... and where else better to ask than here .
Archie Moore George Foreman Larry Holmes Jersey Joe Walcott (genrally accepted that he lied about his age)
Ray Mercer was over 40 when he fought Wlad for the WBO belt. Obviously Evander Holyfield, for the IBF belt against Chris Byrd and last year for the WBO belt against Sultan Ibragimov. Oliver McCall fought two title-eliminators for the WBC belt recently, does that count?