I'm already in my early 50s (today is my 51st birthday). One of the things I've learned after a couple of years of trying to build a startup is that I
love working on my startup. I'd put twenty years into a career in enterprise IT, and it made me miserable. I realized that it's not the work itself I don't like - it's working for others, working on things I think are stupid and pointless and doomed.
The problem is this means for now, I'm working two jobs, and I'm heading for a rough transition to working just one and the financial implications of that. That's a lot of stress.
On the other hand, doing a job I have come to despise until I'm too old to do it anymore, instead of doing something that matters to me, that makes me feel meaningful and accomplished... that's a whole different kind of stress. That's the kind that grinds you down and wears you to a nub. Once you hit a certain age, perspective really starts to set in. I look around at people in their 40s and 50s, and they're broken. They think their best years and best opportunities are all behind them. I look at mine, and they're ahead of me. That keeps me alive.