Adam Horwitz first caught the start-up bug at age 15, but there was just one problem: No one took him seriously because of his age.

Three years and thirty or so failed start-ups later, he launched Mobile Monopoly, his first successful product. He followed that up with YepText, a service that provides small business news via mobile text message. Now he's reportedly working on Young & Boss, a social network for young aspiring CEOs.

According to CNN Money, Horwitz's main motivation was simple: Start a million-dollar company before he turned 21. 

“All of my friends were doing babysitting jobs. I wanted money without the job," he told JuniorBiz

In a way, being young actually worked to his advantage. Horwitz found he could more easily market to peers, because he understood what they wanted, and since he was living at home, every penny went straight to the bank. 

His advice to up-and-comers is simple: "Even if you fail the first time, who cares? The worst thing that could happen to you is that you wake up and go to school the next day. So just keep at whatever you’re doing and I promise you you’ll hit it."