No, it's not normal for a normal corn, but it's normal for the one you got. There are probably internal reasons he was so tiny to start with & is unable to grow at a more
normal pace...maybe an undersized stomach or some sort of GI tract stricture that limits what he can comfortably digest; also his low "ridiculous" price suggests that the
breeder/seller knew this when you got him, and you should have suspected or asked more questions. From what I can see in the photo, his body weight looks to be in
correct proportions- ie. he doesn't look starved or overweight. I'd just accept who he is & feed him according to his needs. In case this is genetic, I would not breed this
guy either, just enjoy him as a pet. In nature, not all are created equal...and "good things do come in small packages" too.