They do realy move up fast on mice sizes, that's why most people feed rats, since they get much bigger. Im raising 2 babies, they are about 3 months old now. They eat the smallest small rats I can find, Which are about the same size as a grown adult mice.

Try giving him a medium mouse and see the results for your self. Im sure it will be fine. He could probably take an adult mouse too, but you would know better =)