The best advice I can give is to keep offering him rats at every feeding. If he does not take the rat, then pull it out and offer him a mouse. Some ball pythons will never convert to rats. I have a few in my collection that never would convert. I had to settle on feeding him lots of mice. On the flip side, keep your chin up, as I do have two female balls that finally took rats after they were a year old. They now eat nothing but rats, but my persistence finally paid off after a year, I just kept offering rats, and it finally worked. Ball pythons will be Ball pythons, they eat what they want when they want it, and there is nothing you can do about it.

Good Luck,