As someone else asked - pinky mice or pinky rats? Makes a huge difference.

When mine were close to hatchling size, they were eating a mouse hopper a week, and then after a few weeks bumped them up to small mice, and gradually up to medium/large adult mice.

I can remember being nervous about going up in size with my first ball python, each time, so I can understand your hesitation, but if he's otherwise healthy and eating for you each week, there's no reason not to try him with either a small adult mouse or a small rat pup each week.