I’d expect it to stratify based on the kind of business.

Typical small businesses (plumbing, HVAC, restaurants, convenience stores) I’d expect to come from poorer families. These businesses are a potential avenue to success without traditional credentials, and they’re not the sort of thing somebody is likely to start as a passion.

From wealthy families, I’d expect vanity businesses. There wouldn’t be as much motivation for the annoying aspects of a real business. And anyone who is interested in business can probably get a nice start in something their family owns or has a major stake in.

Moonshot companies I’d expect to come from the upper middle class, children of doctors and such. Not fabulously wealthy, so the potential for making millions can still be a big motivator. But comfortable enough to get advanced schooling and be willing to aim big with a chance of failure, rather than going for something mundane you know is always in demand, like fixing pipes.

Off the top of my head, Gates, Page, and Zuckerberg all fit that mold.