iunno man they've never been very clear about how he works. by the end of the show he's 17 and that's dang old for a dog but he seems as spry as ever. And yeah he's magic, but Jermaine isn't, and he's 17 too. He has access to a lot of arcane crap I suppose but he doesn't seem the type to artificially extend his life
on the other hand these are commissions so it's best not to take any of it too seriously, he's mixing canons all over the place.