Most of these nine entrepreneurs had launched businesses by the tender age of 16 (and one before he broke double digits). Some identified problems and created companies to solve them; others turned their hobbies into moneymaking ventures. Some teamed up with friends, siblings and mentors; others plowed ahead on their own.

• Video: Turn a hobby into a business (part 1)

• On Bing: How to start your own business

Their common threads: singular focus, preternatural financial savvy and the optimism and confidence to wrest financing from seasoned investors. Here's how they did it.

Continued: A new vision