Sixteen strikes me as a good age to define as "late", but anything around that age can qualify. All eras, all weight classes. Go.
The prison guys start late. Clifford Etienne took up the sport in prison (I think), same with Ron Lyle. Getting started in their 20's.
hopkins as the obvious answer. Matt skelton from uk started at 37 and managed to get a title shot at hw
hopkins started pretty old. Nate Campbell as well. Cintron started at 19 but hes a little ***** so he doesnt count.
hmm says... Chavez Jr.'s first fight at 18 but he's not great..... Rocky Marciano's first amatuer fight was at age 23..... that's if I'm correct
Dwight (Braxton) Muhammad Qawi- did not start boxing untill he was in rahway prision in NJ, and turned pro upon his release.