What does the average entrepreneur look like? A 40-year-old cubicle refugee.

    By Ian Mount

    (Fortune Small Business) -- Bill Gates. Steve Jobs. FedEx's (FDX, Fortune 500) Fred Smith. The image of the entrepreneur as whiz kid has serious currency in American business lore. But according to a new study from the Kauffman Foundation, a Kansas City think tank that studies entrepreneurship, that image is a myth.

    For "The Anatomy of an Entrepreneur," the foundation surveyed 549 company founders. Instead of a dorm-room genius, it found that the typical founder is middle-age -- 40, on average -- when launching a first company. Seventy percent of first-time founders are married; nearly 60% have at least one child.

    They're also a study in class mobility: 59% come from lower-middle-class or blue-collar families, and almost half hold advanced degrees.

    "The commonly held belief that entrepreneurs are young college students working out of their dorms is simply wrong," says study author Vivek Wadhwa of Duke University's Center for Entrepreneurship and Research Commercialization. "People typically come to a stage where they're tired of working for other people. They think, 'I'm 40 and I haven't made it big yet. This is my last chance.' That really spurs the entrepreneurial spirit."

    Wadhwa knows from experience: Before entering academia, he founded a technology company -- at age 39.