Availability heuristic and confirmation bias. It's not big news when someone who's 51 strikes it rich, but it's unusual when someone 21 does. So that what gets reported and that's what comes to mind when you think of starting a company. If you looked at the news you'd think everyone who's rich got there by starting a hot startup in college (or got a big Wall Street bonus), but it ain't necessarily so. Take a look at books like "Millionaire Next Door" for some more balanced info on the kinds of companies people start and what age they become wealthy.