Rodent Care

We have a mouse who is roughly seven months old. He's a good little mouse and likes to be held and played with.

I clean his cage every three days or so to cut down on the smell, though he isn't nearly as stinky as a hamster or gerbil. However in the last couple of weeks, I will clean his cage and the next day it smells like I haven't cleaned him in a week.

Also when I take him out of his little floor ball, that thing smells so bad I can barely pick it up to clean it.

Could there be something wrong with him or is he just aging?

BTW: He's eating well, is still sociable, and plays normally.