Jessica Mah
inDinero, Mountain View, California

Forget, for a second, that Jessica Mah is an anomaly.

Forget that as a 20-year-old female CEO who is also an accomplished software engineer and who just raised more than $1 million, she is, in the words of the investor Paul Graham, "so statistically unusual that there may not be any other CEOs like her working today."

Those facts make Mah different -- and amid concerns in Silicon Valley about the lack of female entrepreneurs, maybe even interesting -- but what makes her extraordinary is her prodigious and unabashed drive. Mah's young life has been a study in doing more than seemed possible, faster than seemed possible, and her achievements are a rebuke to every tossed-off complaint about Kids These Days.

Mah left high school early to enter a precollege program and then graduated from the University of California, Berkeley, at 19. ("School is kind of boring when opportunity awaits," she explains.) In her final year, Mah and a friend, Andy Su, began working on inDinero, a website that makes it easy for small businesses to keep track of where their money is going.

That a teenager would become interested in small-business accounting might seem strange if the teenager in question hadn't already started several small businesses, including a Web design company (at 13) and an internship listing service (at 18). "I'd noticed that anything that touches money is much harder for entrepreneurs than it should be," Mah says. She decided that part of the problem is overly complex accounting software. "QuickBooks was really innovative 20 years ago, but they've hardly improved the product since then," she says.

In June, inDinero entered Graham's Y Combinator mentoring program, and Mah took her product live just one month later. By September, she had closed a $1.2 million angel investment round that included YouTube co-founder Jawed Karim and the seed fund 500 Startups. Today, inDinero has seven employees and 6,000 customers, who pay from zero to $100 a month, depending on the number of transactions the company tracks. "Jessica is a machine," Graham says. "She's going to win at whatever game she plays. The biggest danger for her is going to be figuring out which game to play."

It's not a bad problem to have, but Mah insists she is not in business for an enormous payday. "It's not a means to an end," she says. "We're having a lot of fun in the process." She and her team, most of whom share a four-bedroom house in Mountain View, are working from 10 in the morning until "midnightish." Mah calls the hours "very reasonable."