The only real reason why it's harder for older people to make a startup is the high risk involved. Once you have a family you cannot mess around anymore.
But I've seen the "wife has high paying job with steady income, husband is kinda fly-by-night" pattern often enough that I wonder if other people see it too.
I never did find that kind of a women myself. Damn!
That said, let's make the wild assumption that some women might be entrepreneurs, and rephrase this as: Isn't it the responsibility of the spouse to bring in a steady income?