This is important. There's a big difference between getting started at 45 and founding your third company at 45.

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.