For my startup, age is crucial: There's no way I could have done this work before I was 40, and similarly for would be competitors.

I had to learn about:

mainline business

entrepreneurship

startups

venture capital, what it is good for and what isn't

about people, especially in business -- vendors, employees, customers, investors, lawyers, management, organizational behavior, etc.

quite a lot of pure math

quite a lot of applied math and associated computing

my original applied math

The pure and applied math is Ph.D. stuff, and I do have that Ph.D. But some serious business experience is crucial. Just those two prerequisites rule out nearly anyone under 30.

But, but, but, people over 40 are out of new ideas? Not in my startup!!! The user interface, user experience, some of the computing, and especially the crucial core enabling applied math are far out, wildly new, "radical, provocative" stuff.

If I gave a lecture on the custom, internal ad targeting applied math, then nearly everyone in Silicon Valley, entrepreneurs and VCs, would soil the furniture and then, on the way to the restrooms, the carpet. Later they'd meet at a local bar, try to wash away the shock, and try just to f'get about that experience. Why? As I learned as a first year pure math grad student, there is little so intimidating, frustrating, confusing, and discouraging as a very nicely done, precise, fully correct, advanced, strikingly original, calm, lecture on pure math where understand only a key word now and then!!!!!

I do owe a thanks to the author, Irving W-B: At one time he invited me to give, and I gave, a very simplified version of just such a lecture on some of my research to some of his people!!!! What I gave then a colleague had pronounced "radical, provocative". After my lecture, some of Irving's people and I had lunch, and on one small point agreed that I'd reinvented k-D trees, IIRC in Sedgwick.

Think people over 40 can't be original? Ever hear Wagner's <i>Tristan und Isolde</i>?