Actually, white spots on a Betta is not natural with age. It most likely means he has Ick. You can buy Rid-Ick (or something like that from Petsmart) to help cure it... Ick can definitely be fatal and it spreads very easily to other fish.

Bettas can easily live past 3 years. I had an almost 4 year-old Betta, and Kara had a 5 year-old, I think ... He's probably around 1 1/2 years old at least, because pet stores usually don't sell Bettas until they're at least 6 months.