I think the "average" for males tends to be 3-4ft anyway...so it could be that no amount of feeding him/good husbandry will make him grow. It's the females that get on the larger side--and even then, there are no guarantees that they'll get 5+ feet.

Though if he was in a bad place before you bought him, I'm glad to hear that he's come to a good home and that you intend on keeping him in better conditions