To be honest, I don't know how old my betta fish are when they die because I can't age fish. All I know is if I buy a sick fish, he'll live for about 6 months to 1 1/2 years under my care (which is part of the reason why I stopped rescuing). When I buy a healthy fish, it last about 2 to 3 years (but usually two years ^_^;).
However, for the sake of guessing, Luigi was probably 4-ish years old when he passed. I've heard of fish living for 7-10 years, but I've seen in happen in one of my tanks. XD