Welcome...
Don't worry, ball pythons don't get stunted. If they were underfed, generally they will eat like pigs until they get caught up to where they want to be and then they will back off. Most of my adult males will eat one small rat every two weeks if they are not being bred, some more, some less. Most adult males also will go off food for 2 to 6 months a year. Breeding animals, I try to get to eat weekly. Keep in mind that boys are usually much smaller than girls. That said yours does sound small for his age. Shoot us a picture and we can get an idea of his build and then maybe you will get a better opinion.