As long as they are eating regularly, shedding, pooping and peeing, then the rate at which they gain is really not that important. Given that the factors I just listed are in balance, they will gain as much as they are able to gain. Some will gain fast, and others will gain a little more slowly.
My personal theory is that all baby ball pythons are genetically wired to be good eaters prior to reaching breeding size/age. This programed instinct gets them bigger quicker which accomplishes two things 1) Gets them off the bottom of the food chain quicker 2) Gets them to breeding size faster so they can pass on their genetic material to the next generation.
But, deversity being what it is, they will always grow and gain at their own pace.