My sister's betta was bought when he was full grown - but he has still lived for 2 1/2 years since then, and going strong! He's absolutely huge - I've never seen a betta with a head like his, he looks like a salmon with his great hooked jaw and all.
Ok well I've answered this in another post. In books they say around 2 years. However if you know what yoru doing and they are in good conditions they live to around 3-4 years. Mines been around for 3.5 years and its healthy.
