Ray Mancini retired at age 25 or something. I know a lot of that was because of the tragic death of the Korean fighter.

He did return to fight Camacho in a close fight.

Its hard to think of guys that left too early, Danny Romero springs to mind I suppose.

Kassim Ouma too. He beat Vanes Martisyan and got robbed, which I'm sure was discouraging.