How does a guinea pig die at 3 years old?

Every guinea pig is different. Some live to be 15 others don't even live to 1 year old. It's all about how they got cared for. If you clean it's cage every other day, groom it, give it a bath every so often, and give attention, it will probably live for a long time. It all depends on how it was cared for. And every guinea pig is different. How well a guinea pig is cared for plays a major role in its overall longevity however that is not the only factor. Many guinea pigs become victims to genetic diseases which are not your fault as long as you took it to a vet and it received the best treatment possible. Always keep a hawk eye on your guinea pig's health making sure to check for any sores, abcesses, weight loss, change in behavior, or stool/urine changes daily or as frequently as possible.