Like so many successful entrepreneurs, Sean Belnick came up with his great big idea after watching what other companies were doing wrong. The only difference is, in his case, this eureka moment happened to come at the age of 14.

While hanging around his stepfather's office at a furniture manufacturer, Belnick noticed something interesting. Retail furniture stores would call Belnick's stepdad to place an order, which was then shipped directly to the customer. Why not save customers a trip to the store -- and the headache of dealing with high-pressure furniture salesmen -- by creating an online marketplace for office chairs?

And thus, was born. Belnick, who had already cut his entrepreneurial teeth building websites and selling Pokemon cards on eBay, started his direct-shipping company using a Yahoo store account to facilitate the transport of his stepdad's furniture orders to customers. The idea required virtually no start-up cash. "That's the beauty of the direct shipping thing -- there really was no funding needed," says Belnick, now 20. "I basically took $500 in advertising, and it snowballed from there."

Originally, Belnick launched the company from his bedroom with an inventory of 50 to 100 products. Six years later, has 75 employees and sells more than 25,000 products from some 200 manufacturers. That $500 investment turned into $24 million in revenue last year. The company has expanded beyond the direct-shipping model to stocking many of the products it sells in a newly opened 327,000-square-foot warehouse in Canton, Ga. In addition to office furniture, the site now offers home furniture, school furniture, and medical equipment. Most items sell below list and are shipped for free -- made possible, in part, because the company doesn't have to operate brick-and-mortar stores.

As the top result in a Google search for "office chair," has attracted a wide -- and indeed, high-profile -- customer base. "We sell to your next-door neighbors, we sell to businesses, we sell to the Pentagon," Belnick says. Other notable clients include Fox's American Idol, Microsoft (NASDAQ:MSFT), and yes, Google (NASDAQ:GOOG).

When he's not in the CEO's chair (pun intended, of course), Belnick studies business at Emory University, where he is entering his junior year. Although his schoolwork keeps him from maintaining the kind of hands-on role he prefers, during the academic year Belnick is still very involved in the higher level affairs of the company, especially in the marketing and IT departments. (His stepfather oversees day-to-day operations while he's at school.)

Belnick says he's looking forward to the continued expansion of the company, which will include stocking more inventory and moving into other furniture markets. He's also excited about graduating college. "I can devote a hundred percent of my resources to it," he says, "when I'm not in school."