It's breeding season and he's two years old...going off feed is normal. Wait a week and try a scented rat. Especially if he's been eating mice all this time he probably doesn't recognize the rat as food, since they smell much different from mice. I've had fairly good success with scenting, if he doesn't take it I'd still offer every 1-2 weeks as normal and just stick it out through breeding season. Keep track of his weight.