In The Lord of the Rings: The Fellowship of the Ring, it is shown that Bilbo keeps the ring for almost 60 years, not as much as Gollum (who kept it for centuries). But still Bilbo remains totally unaffected by the powers/burden of the ring. Why didn't Bilbo develop characteristics that Gollum developed? Is it something I am missing here? Kindly help.
First of all, the possession of the ring didn't stay entirely without effect even to Bilbo. Remember how everyone was surprised at Bilbo's apparently unaged looks compared to his actual age (and his pretty fast aging once he didn't have the ring anymore). And also remember his reluctance to give up the ring (into which he had to be seriously "persuaded" by Gandalf) and his "outburst" in Rivendell when he caught a glimpse of it on Frodo's neck (a scene that made me jump in my seat on the first view and that still terrifies me whenever I see it). Those effects might very well have worsened if Bilbo would have kept the ring for longer.
But another important aspect is, that Gollum is a morally weaker person to begin with. After all the ring for him was won in an act of evil in the first place, murdering his friend for the "precious". That is something we could surmise Bilbo wouldn't have done, as evident from the mercy he showed Gollum -- a supposedly disgusting creature he didn't even know -- when he had him at the point of his sword after stealing his ring. But he saw what a miserable creature Gollum was and felt compassion for him.
Then add to this, that Gollum is also pretty much a product of his circumstances. When he killed his friend he became a social outcast, which even more contributed to his further moral degradation and his alienation from "normal" social life. His split personality might on the one hand be just a natural result of his loneliness but might on the other hand as well be a way to cope with his deeds, first and foremost the murder of his friend, either by said friend manifesting as the second personality or just as an attempt to blame his deeds on that "other person" living inside of him. And the fact that he became a cave-dweller far from the sunlight eating raw fish and orcs and whatever vile creatures might have contributed to his further physical deterioration. Bilbo on the other hand still lived a happy life as an accepted member of a blooming social environment so that the ring couldn't unfold its whole potential on him, but after all we also know that if the ring has anything, it's patience.
Gollum was a Hobbit, or rather a predecessor of a Hobbit, but was kicked out of his clan and forced to live in a cave. He became almost immediately obsessed with the ring; in fact he killed his friend who had originally found it. Gollum was weaker than Bilbo; the ring completely controlled him from the get-go.
So, the major differences were Gollum's weakness, and his living conditions which made him anti-social and changed his appearance due to the absence of light.
Bilbo definitely was affected by The Ring, just not to the same extent.
I agree to everything said in previous post. I always imagined that Gollum became the way he was because he wore the ring extensively. In the Lotr's book Gandalf would warn Frodo to be careful as to not to use the ring. The ring had less effect on Bilbo because once the adventure in "hobbit" was over Bilbo stayed in the Shire, there was no need for Bilbo to use the ring. But still, since he kept it he didn't age and obviously grew attached to it. In the book it clearly says that Gollum used the ring as soon as he found it, he liked the way he was invisible to everyone, but at the same time it also upset him.
Don't forget the differences in time between the movie and the Tolkien's books.
In the book at the Birthday Party, Bilbo was 111, and Frodo was turning 33, the coming of age for a Hobbit, also part of Bilbo's joke, a gross of guests and the sum of both their ages 144.
17 years pass in the book before the journey to Bree begins, making Frodo 50, "coincidentally" the same age as Bilbo was in the Hobbit, and Bilbo 128. The Ring had been away from Gollum for 78 years at that point, and Sméagol had also been under the care of the Elves for a number of years just like Bilbo.
Personally I always thought that the mountains that Bilbo wanted to see, were not the mountains of the dwarves, but the mountains surrounding Mordor. His subconscious was being driven to take the Ring to Sauron, the same way that Sméagol was driven to hide the ring and keep it safe until Sauron could reconstruct himself. Or was Gollum keeping the Ring for himself away from Sauron? Perhaps Gandalf had something to do with Sméagol as well, was not "Keep it secret. Keep it Safe." also what he told Frodo. It might be Tolkien wanted Sméagol to be more tragic and more heroic than made out to be.
The answer is not given in the movies, but, as another commentator noted, it was given in the book. Because Bilbo began his time with the ring in an act of kindness (not killing Gollum when he had the chance, but showing him mercy and compassion instead), he was protected from the worst of the ring’s influence.