They are barely out of college.

But internet start-up entrepeneur Drew Houston, 28, and girlfriend CeCe Cheng haven't wasted any time getting on the career ladder-the young couple have just become Silicon Valley's newest young billionaires.

Houston's four-year-old file sharing and storage company, Dropbox, the online data storage company, is on the verge of closing a major financing round of $250 million to $300 million.