It takes 10 months to save $40,000 if you're putting away $4,000 a month (which is half of take-home pay at $150k). If you are someone smart enough to be an entrepreneur in your late 30s with a corporate job paying 150k+, your children are probably smart enough to want to go to an expensive college.
Looks like it can be done for quite a bit less than that, when ACA subsidies are taken into account (or when expanded Medicaid is taken into account if the other adult family member also has no income...I think all the states where tech startups are common went along with expanded Medicaid).
To get through college for $10k/year in many places, you'd need to go to one of the state's lower-tier schools in a small town and live at home. Not many state flagships are in the business of charging less than $20k.
Unfortunately, without working more than 20 hours/ week, a college student isn't going to be able to come up with that $18k per year on their own, but they could get more than half way there, which doesn't leave a ton of support the parents would actually have to provide.
She does live at home. If she lived at school it would be about $17k
And health care, while expensive, isn't as big of a deal as most people make it out to be. Get a high deductible plan and a family of 4 can be insured for <$700/month. If you are starting a business in your late 30s you should have a lot of savings already. While annoying, this shouldn't stop you.