Don't worry about the age. It's nice to know when x was born or hatched. You bought a young one around x months old. The important thing is you weighed him. So go read this:
https://ball-pythons.net/forums/show...=feeding+guide
It's not the end all but it's good. When my BP's hit 500g (sometimes sooner) the feeding goes to 14 days, before that I use 10 days. It was beaten into my head in the 70's slow is good an fast growth is bad.
Oh, PetSmart snakes are a month or so most of the time. Well, that's what I've been told.
Good luck!