Are you sure? Is it not the same as this: https://math.stackexchange.com/questions/1009490/average-num...

E = p/(1-p)

So pretty close to 80 years, no?

I guess it gets more complicated because you'd die of other reasons as you age so there's no point including the eventualities where you reached 120 for example... I guess it gets pretty complicated in the end...