Marry an American, get citizenship, then go found your startup. And never, ever think you're too old.
Your situation sounds a lot like my dad's. He came here after college, finished his Ph.D in the U.S, then got screwed over in every industrial position he took. The immigration situation sucks in this country. You need a company to sponsor you, but the company realizes that you have zero leverage as a foreigner, and treats you accordingly. He was paid less than native-born citizens, missed out on all the scientific conferences given abroad because he couldn't leave the country easily for visa reasons, and found that promotions and accolades went to his American colleagues that knew how to work the system, rather than the people who did the best technical work.
He ended up getting his citizenship when he married my mother, a few years past 30. But in a sense it was too late for him by then: he was so bitter about the way he was treated in industry that it poisoned all his future ventures. It did mean that my sister and I grew up as native-born U.S. citizens, though, with all the cultural capital that comes with that.
My advice for now: forget about the startup. Instead, concentrate on learning as much about American culture as possible. Go out with coworkers after work. Start cultivating your own social life - invite friends to go do stuff with you. Date some American girls. Listen to pop music. Someone said throw away the TV set - I'd actually disagree with that, I think you should watch more TV, but don't just veg out. Instead, listen carefully to what shows the people around you are into, and then watch them so you have something to talk about with them.
This'll all be useful if you ever found a startup in the future, but more to the point, it's essential if you really plan on staying here permanently. My dad never fully assimilated into American culture, which meant that my sister and I had to pick up a lot of it as kids, sometimes very painfully. And then it caused conflict with my father, who remained very Chinese (and distrustful of Americans) until he died. If you stay here, you'll need to interact with Americans wherever you go, you'll need to rely upon them to build a business, and your kids will become American. Better to join them than fight them.
It's very easy for non-foreigners to forget just how much of an advantage cultural capital gives them. There's this huge iceberg of cultural skills that white middle-class Americans take for-granted, that are just unknown to foreigners, poor people, minorities, or children of foreigners. You hear these stories about immigrant entrepreneurs who hit it big in America - but if you talk to any of them, you usually find that they mastered the culture first, and then founded their companies. It's not a matter of "the smartest engineer wins"; it's a matter of "the smartest engineer who acts and talks like me and that I can feel comfortable doing business with wins".