i am by no means an expert in ball pythons, but i'll try to give as much advice as i can
if the snakes a couple inches shy of 2 feet it could be a yearling, perhaps one that wasnt fed that well in its first year, or perhaps a runt
it sounds a bit skinny if its only 1.5 inches in the thickest part of the body. Load her/him down with some food and see if you can put some weight on it
i'd say a couple adult mice a week would be good for that size my ball python's a bit shorter than that and he takes 2 adult mice a week (f/t adult mice)
hope i've been of some help and sorry in advance if i have given any misleading advice i'm still somewhat new to ball pythons myself as well
James