Facebook, behemoth that it is, is still a startup. We get a little carried away calling every little personal website project a startup and perhaps that's just right for the forum. But don't get tunnel vision. Facebook is a startup.
If you have more money privately invested than money earned, you're probably a startup. If you're searching for a repeatable, scalable business model, you're probably a startup.
Or, your business might be a failure, yet past the point of being a startup. Clearly Facebook does not qualify as a failure, but they are not a startup in my estimation. They're an established business.
It is pretty arbitrary and Facebook is a late-stage startup but hundreds of employees, sky-high valuation and five years of age are not unheard of and still within 'startup' range, to me. Mushy factors include things like culture, innovation, risk. I'd say 'run by founder' also adds startup points.
I would suggest stock value more than 50x peak profit probably works. A 5 year old billion dollar company that is never made more than 1 million a year is probably still a startup. A 3 year old 10 million dollar company that made 500k last year is probably not.
Only if it's valued more than past revenues would suggest. IMO, Tesla Motors is still a startup Google is not. What separates them has more to do with the stability that comes from profit than it does an IPO or company culture.
Good thing he's not going to a startup, he's going to Facebook.