Hi everyone

I have a question about the growth of ball pythons. Its not about mine, but about my friend's. He got his ball python in november at slightly larger than hatchling size. He's been keeping it in a 20 long aquarium, with a heat lamp and heat pad, aspen bedding, and some plants and hides and water bowl. He started off feeding it on mouse fuzzies (which i told him were too small), then he started giving it 2 fuzzies, and just recently on rat pinkies. Weird thing is, it doesn't seem to have grown much at all. Maybe a couple of inches. My ball python grew a foot from 3 feet since i got it late november last year at already 4 years old. Anyone have any ideas of why this is occurring?