Elder sim living well beyond his years....Will not die

I also have an immortal sim. He was created in CAS as a neighbor to my main household. He worked in fitness and had a high fitness skill I believe. He's still alive in my game seven generations later. I've tried deleting his entire household, too, and it just reappears in my game again. He always comes back and I have no idea how. lol.
Anyway, yes. I think there's a glitch somewhere with the game.