Pinks & hoppers are not appropriate-sized meals for most 18" ball pythons. At a foot & a half in length, your snake should most likely be eating adult mice or rat pups. It is OK to feed your ball python a meal that leaves a small but noticeable bulge in it, especially as it's young & growing. You don't want to overfeed, but you don't want to underfeed, either.

Feeding a ball python that size a pinky is like you sitting down in anticipation of Thanksgiving dinner & only being served a CheezIt.

Make sense?

K~