Elon founded Zip2 right out of undergrad, Garrett Camp founded StumbleUpon while in grad school, and Kalanick left UCLA undergrad to found Scour and then kind of expanded on that with Red Swoosh right after.
Most of these are still accurate and it's really cool data, so thank you for posting; just figured it was worth commenting on nonetheless. :)
I don't think there is something biological, or even social that makes it hard to be a late-bloomer in tech entrepreneurship. It's just hard to develop an entirely new skillset and network in later-middle age. I think we'd mostly be skeptical of a doctor who started medical school at 45, and while the stakes for founders aren't as severe, the same principle applies.
You probably wouldn't be sceptical of a managing director of a medical research company who'd dropped out of med school when they reached 10+ employees.
To leave age out of it, the study shows that those who successfully founded growth companies already had the skillset and network to draw on. (Perhaps the older ages were due to the years it takes for someone build their skillset and network?)
Musk could build Zip2 at 24. I would say there's zero chance he could have successfully built Tesla or SpaceX at 24 (ignoring the capital requirements). I think that far more often than not, to start and build great companies, requires a small lifetime of accumulated experience and mistakes.
The media myth of the tech industry and its important companies being founded by 19 year old Zuckerbergs, is just that, a myth. The media loves that story because it sells, it's just not real.
I'd like to think that most successful founders fail at their first few not so noteworthy "side-projects" before finding success and sticking to it. Just building a crappy version of something not-so-cool can teach you a lot about tech, business and design, which then helps you build better products in the future.