I've had a Betta for a few years, but I don't know that he is really old. He does look older than when I got him...think tired old farmer.
i've noticed lately his fins look like they're thinning and getting shorter. It's possible that he's being nipped, but I have a clown loach and a chineese algae eater, and I've never seen them nipping. Chasing, maybe, but they've done that forever. He really doesn't look sick...just old. So I'm wondering if his fins are sign of aging, or if he's sick and needs to be Qd and treated.