I've heard that if you look at _successful_ startups, not necessarily unicorns but ones that grow into solid companies on a firm financial footing, the average age of the founders was in the middle 40s.
I would wager a guess that if you actually based success on revenue/employee, operating margins, and overall "healthy" business criteria, the number skews probably even higher.
As we were clearly made aware of in the last year, many unicorns of the last 5-10 years were little more than good marketing and a Tier 1 VC footing the bill.
