Has anyone attributed hair loss to old age?

My parents 13 year old black cat Reebok has a large patch of hair loss on his belly between his hind legs. The fur is really soft, like it's regrowing from a shave.

No sign of iritation and there have been no recent changes in his lifestyle. He's just a laid back guy that's content on your lap. So we don't think he's obsessively grooming.

Negative for parasites and mange.

It's just odd.