I do think that smaller, older animals can be stunted. I've had slow starters that just didn't grow while being assist fed. Even after they began feeding on their own, they did not grow like others. When I see smaller animals, I chalk it up to lack of food, whether it be inconsistent feeding, too small of meals, or reluctance to increase the frequency or size of prey items. Most kingsnakes should be 30-40" by 12-18 months old.

Either way, as long as they are eating and healthy, you should be fine.