Samwise: 62. How precisely that translates to human ages is iffy. They have a lifespan just slightly longer than humans, but regard their 20s/early 30s as childhood. He was a young adult at 38 when he quested with Frodo (50 at the time). I aim for mid-late 40s in how I play him.
Peter: As old as the concept of childhood, but he has such a slippery grip on memory that the past 200-300 years are all he's got, and that is really mostly just a neverending now.
Erik: Smashing the timeline of both books together, he's at least 82. (Creature comes to life in November 1792, the events of PoTO happen in the 1880s.)
(Creature comes to life in November 1792, the events of PoTO happen in the 1880s.)