There are many reasons that startups tend to have young employees.

As someone in a similar place in my life, I'd never take a job like that either.

Yeah - financial risks aside. It just seems difficult to do this without major disruptions to family life as I am a part of it. Of course, you can hire as many people as you need (if you have the means) to resolve the logistical problem. But my absense isn’t replaceable like that.

I expect not really? I'm 42, married, but no kids. I can't imagine joining an early stage startup. Not just for the kinds of reasons you mention (being present in a marriage), but just because it sounds so exhausting. When I was 30 I could pull an all-nighter and still have a somewhat productive next full day at work until I could finally get some sleep that evening. But these days I'll be a passed-out wreck by 10am, at best, assuming I even make it through the night, and will feel like shit for a couple days afterward.

There's a reason why people in their 20s or early 30s, and/or without a partner or kids, are over-represented in early startups. When I was deepest in my startup work as an employee, I had no time to date, and didn't bother to try. My friends barely saw me; most of the little socializing I did was with my co-workers, and that socializing often felt more like work than play, as we were usually discussing (or complaining about) work.

I do know people our (current) age, with families, who have done it, but I frankly have no idea how, and I'm sure it put a strain on their marriage and on their relationship with their kids.

On the flip side, as someone who has no kids (and doesn't intend to have any), I have noticed a lot more tolerance for missing work / missing meetings / ducking out for a while when it's for childcare than for any other reason. But a childless employee is seen as having no excuse for needing time out of the office here and there for whatever reason. (I suppose this is true to some degree of both startups and established companies, though.)