I sold IndexTank to LinkedIn among other things.
It was a gradual process for me that started with the first dot-com boom. It wasn't as big of a deal as I thought it would be.
I was 41.
Cashing out stock from public companies I've been at, selling consulting services before building IndexTank, selling IndexTank.
I don't think there is such a thing as overall happiness. I do live in the present more than I used to, but that's perhaps because I'm older. I do worry less about certain things, but the "worry hole" is always there asking to be filled. We all age, get sick, have family / relationship problems, need to stay motivated. I almost certainly enjoy life more than I would if I were forced to take an unpleasant job, but there are many other things a person can do to make life enjoyable besides trying to win the startup lottery.