No, Sméagol and Déagol were effectively cousins, and Déagol, too, wanted the Ring as he found it. They both fell under its spell, and that's why they started fighting, which ended with Sméagol drowning Déagol.
Hobbits do live longer than humans ─ Bilbo was well over 100 years old by the time Frodo, Sam, Merry and Pippin set out on their journey. But indeed, Gollum's age was unnatural and caused by the power of the One Ring.
Yes, that's exactly how it was.