His peak was probably lost in Mighty Mick's Gym fighting bums. He was never closer to his peak on film than he was vs Spider Rico. Who knows what he could have done if all he had to do was fight for a living instead of act as muscle for Gazzo.

Rocky was 30 when he fought Creed. Rocky being that certain style fighter he would have probably been in his physical prime about 5 years earlier, HOWEVER he completely changed his style several times. In Rocky II he learned to fight in the orthodox stance, in Rocky III he learned to be a slick boxer, in Rocky 4 he forgot all that and went in face first again....so that means Rocky has always been a boxing prodigy but he's also prone to fighting like a dumb fuck. It's like he could fight like Floyd Mayweather but was more comfortable fighting like Arturo Gatti