A little advice (rat owners)?

well, he is pretty old. since he seems happy i think you should wait. but i hope it isn't a tumor. i would get it checked out by the vet to make sure you know what it is. but, at least he is happy. :) i'm glad to see a person who cares so much about their rats. Most people i know wouldn't care much about it and wouldn't be willing to spend the money on their pet.