Well i think you have to look at the intention of the ring-owner as the ring has different effects on who owns it. For example bilbo had the ring for 60 years or so and gave him the ability not to age, frodo bears the ring for a few months and is transformed completely differently, the ring is heavy and causes physical and emotional problems for frodo. For gollum the ring's presence caused him to kill his friend... jsut another insight that goes along with most of those already posted.
The Ring's effects were also influenced by Sauron's power at the time and proximity to Sauron. The Ring had such a dramatically stronger effect on Frodo because Sauron was becoming that much more powerful and he was wandering around in Sauron's back yard.
Gollum, I think, was basically a not very good person to begin with. The Ring pushed him over the edge to kill Deagol, but it was only playing on an existing mental attitude.
A little research on the net seems to indicate that Gollum was probably in his 30's when he found the ring, not 50's. If he didn't age while he bore the ring but started again once he lost it that would put him in his 90's or low hundred's during the War of the Ring, old for a hobbit, but not unbelievably old.