Some people who really take care of/are lucky can keep their bettas alive for four years, I know a few people on here have done it. But I'd say 2.5 to 3 years is a little more common. Good job keeping your finned friend alive for so long
One of my customers has a 5+ year old betta. He lives in a 1 gallon round bowl, sitting on the kitchen table with weekly water changes and fed once per day.
my betta Shyrone lived to be about 3.5-4 years old. So yeah I mean 2-3 is an average though...i suppose the older ones would be the outliers that would throw off that average....AHHH statistics! sorry i have a test coming up anyways yeah so bettas can live a REAL long time...now if i can just get my others to follow shyrone's lead...
It also just depends on the betta. Kind of like people. Some things just naturally die young or live to be a ripe old age. Of course care comes into play, but don't assume that just because a betta dies at 2 that you did something wrong (unless, of course, you did).