The big thing for me is just that the snake eats consistently and an adequate amount.
Now, obviously if we were talking about a 6 year old 5 foot long female, 2 mice ain't gonna cut it. But, since he's still fairly young { you think } and relatively small, 2 mice may not be ideal, but he should not starve on them.
Now, think of a few important clues. Does he eat once a week ? Is he out and hunting for more food within a day or two, or is he content until right before feeding time again ? Is he bigger than when you got him ? Does his backbone stick up prominently giving him a sharp triangular appearance or is it just barley noticeable ?
You can of course try him on a small rat, just a little bigger than his mice for now. If he takes it wonderful, if he doesn't yet, don't fret about it. If you are really worried about him, try offering three mice. If he's still hungry, he'll take a third. If he just kind of pushes it around or seems un-interested, he's full. I do this with all 12 of my snakes, if they are hungry they eat, if not they don't. Now I'm sure there are snakes out there who would gorge themselves silly, but none of mine do. So, start off slow and go from there.
Gale