LogFAQs > #970487303

According to Gandalf's explanation at the beginning of the book, the longer you have the ring and the more you use it, the less human you become. Bilbo has the ring for a few decades, and by the time you see him in Rivendell he's older but it wasn't like he instantly hit a wall or anything. It's more like time is slowly catching up with him. In the book it's been like 20 years at that point between giving up the ring and them running into him again, so it isn't an instant process. He's still a hobbit, he's just been prolonged by the ring but hasn't had it long enough or used it enough to get truly fucked up.

Gollum meanwhile has had the ring for centuries upon centuries and used it frequently. You can even just look and listen to him to see that the stuff the ring does to you has more or less hollowed him out and he isn't anything close to the creature he once was. Gandalf says eventually if you use it enough you'll just become permanently part of the realm of shadows, and although this seems like it must take a reeeeeeeeeeally long time if it didn't happen to Gollum, it clearly twisted him enough that he must have been about as close as you can get before that happened.