It really depends....... A friend told me hers lived for 10 years! Yet some pigs die kind of young like 3 or 4. If they live a happy, healthy life they should live a long time.
My oldest is around nine or ten. And he only recently got nuetered. He is such a happy camper now. He is a black and white silky and his name is Salem.
Mine are quite young still. However, a friend of mine had a pig growing up and it was like 13-14 when it died. I think it all depends on health and genetics.