I think that they can live between 5 and 7 years. I juts love them, they are such wonderful pets. They should be held often so that they are not afraid everytime you walk into the room.
My son's preschool class has two, one is quite tame, the other was never really held a lot (it was donated to the school) and you can tell. It runs to the other end of the cage whenever someone comes near it.
Just remember, guinea pigs needs extra vitamin C as their bodies do not produce it! Make sure they get leafy green vegetables and they also LOVE grass. Take him out in the yard and sit with him while he munches. He'll love it!
Here's an article if you are interested!
http://www.thefamilycorner.com/famil...nea_pigs.shtml