All depends on how much you're feeding him! How old is he? Was 5 his age or in reference to his length in feet? As mentioned by pythons73, each individual snake has a different rate of growth and if he wasn't fed a great deal in his first few years, he might not max out as big as some of the monster sized carpets out there. Though that said, snakes never stop growing, they merely slow down after reaching an average length for their species (esp. length wise, girth-wise is all to do with feeding and a 'fat' python is not necessarily a healthy one).