Most of mine have been anywhere from two to three years old when they passed away. I've heard firsthand of one example of a betta living for five years, and the owners were there for the spawning that produced him, so there was no doubt how old he was. If I remember correctly, he wasn't even kept in what a lot of people consider ideal conditions. He lived in a bowl with no heater and was fed one of the less expensive brands of pelleted food. He was very well loved, though, and diligently looked after in terms of water changes, feeding amounts, and interaction with his owners, so there's something to be said for consistency of care. He probably had great genes, too.