Why didn’t Gollum age when dispossessed of the ring?

Gollum was a BAD hobbit, which means he was much easier prey for the ring than a good hobbit. It could appeal to his greed, resentment, self-hatred, and craziness with no trouble at all! But Bilbo never wanted anything from the ring but the chance to go invisible now and then, and Frodo never needed it or used it while he lived in the Shire.

And I believe Gollum did start aging when he lost the ring, same as Bilbo. He'd been young when he first acquired the ring, and hobbits live a bit longer than humans, so if he'd been normal and healthy he would have aged from youth to middle age during the time between "The Hobbit" and "Fellowship". But since he looked like a wasted freak and not a healthy hobbit like Bilbo, signs of aging were the least bizarre thing about his appearance.

It is interesting. Gollum was completely without the ring for some 60+ years before finally putting it on that one last time in Mount Doom, but it didn't look like he aged at all between the Hobbit and Return of the King.

I suppose the ring had changed Gollum fully in the years before the Hobbit, and he basically couldn't look any worse at that point or afterwards.