Ball Python very small for his age: how do I get him to grow?

[Lstewart]

So I just got my first ball python, he is 6 months old according to the breeder and weighs in at about 120 grams. After getting him I did tons of research and realized how tiny that is for his age, and then I realized his growth has probably been slowed down tremendously due to feeding practices. The breeder kept him on hopper mice all those months he had him, so right after I got him and realized he was still hungry after a hopper, I offered him a rat pup. He took it with no hesitation, and it is just about as big as the widest part of him so it seems to be the right size. The breeder also had him on a 7-day feeding schedule, so should I continue that or maybe feed him every 5-6 days? Just to clarify though, his spine is not sticking out at all or anything so he looks at quite a healthy weight for his SIZE, but not for his age. Does anyone have any tips on how I can speed up his growth in a healthy way? Please, if anyone has any tips or ideas it would be greatly appreciated, I just want to give my little guy the best I possibly can.