A few years ago, entrepreneur Josh Buckley was working on the virtual online world that he invented, when he ran into a database problem and lost a ton of information. He was seriously stressed--but not just about his lost data. The other problem: It was late at night, and he was in the middle of exams. High school exams.

The image of the young programmer, hacking sites and traveling into online worlds is emblazoned into popular culture. But even amid that zeitgeist, Josh Buckley stands out. By the time he was 11, the Kent, England native had taught himself to code. By 15, he was managing 15 programmers, who worked on his sites. Well before he finished high school, he sold one of those sites for what he calls a "six figure" sum.

"I handed my dad the contract [of sale]," Buckley remembers, "and he was like, 'Why are you still awake? You have exams tomorrow.'" He backed off, though, when he saw the number printed on the page.

Today, 21-year-old Buckley runs MinoMonsters, one of the top 100 grossing apps in the U.S. Three million kids play MinoMonsters, he says, collecting teams of colorful monsters and taking them into battles. The company pulled in $2 million in revenue in 2012, and is on track to make $15 million this year.

He’s a long way from his parents’ basement in England. After spending his high school years traveling and looking for projects to invest in--most failed, he says, save once-hot photo app DailyBooth--he relocated to California after graduation to bring his MinoMonsters concept to start-up accelerator Y Combinator. He is Y Combinator’s youngest alum. The company has raised a total of $2 million from outside parties; VC firm Andreessen Horowitz is also an investor.

The funders at Y Combinator weren’t put off by his age. While lots of younger inventor types talk about ideas but come up short on execution, that was never the case with Buckley, says Y Combinator partner Garry Tan, who calls Buckley one of the most "precocious" Y Combinator company founders he’s seen.

Buckley isn’t content to stop with software. When he talks about MinoMonsters’ growth, his favorite brand to invoke is Disney. That’s right: Disney. He knows his audience of young boys is fickle, and he believes MinoMonsters can break free of the gaming world into the lucrative land of licensing--games, toys, books, even movies. He imagines an empire not unlike Rovio’s Angry Birds franchise.

"We’re an entertainment company," Buckley says. MinoMonsters recently signed its first book deal, with Penguin, and the company is represented by Hollywood agency William Morris. Asked about cautionary failures, he mentions Pokemon--a once-popular brand that allowed itself to fade away from popular culture.

Buckley shrugs off his unusual business maturity. When he first arrived in Mountain View, Buckley says, partner Paul Graham took him on a walk around the block. Graham "told me that I was like a 40 year old in an 18-year-old body," Buckley says. "Like the Harry Potter of start-ups."