I have always read the average guinea pig lifespan being between 5 and 7 years, if well cared for. My vet has said that he has treated guinea pigs that were 8 and 9 years old in the past. That said, some are luckier than others and acute illnesses can kill even young pigs. Out of the pigs in my life, my childhood pig lived to be about 7, my older pig, Linney, is still doing reasonably well having just turned 6, my younger pig, Sundae, is 4.5 years and doing well, but Linney's original cagemate, Frenzy, died very young due to dental abscess that got into the jawbone. She was only 1.5 years. The best you can do is good diet, clean housing, and vet care when needed. I think that a lot of people think that guinea pigs only live a couple of years because they don't get vet care when pigs are sick, and many pigs die younger from illnesses that were probably treatable had they seen a vet, or had they seen a vet with a good knowledge of guinea pigs!