Facebook CEO Mark Zuckerberg © Paul Sakuma, AP

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Each year, some Americans make their first million dollars before turning 25, including a few who are still in high school.

Among the traits they have in common are vision, smarts and determination.

A little luck never hurts.

Mark Zuckerberg

"Young people are just smarter," Mark Zuckerberg, now 26, told a Stanford University audience in 2007. Three years earlier, Zuckerberg had helped launch the enterprise that came to be called Facebook and vaulted him into the ranks of the nation's billionaires.

Here's a look at nine other individuals who were millionaires before they were 25, with some of their advice for achieving success.

Michael Dell

Michael Dell, now 45, earned his first million at age 19. Dell dropped out of the University of Texas shortly after starting a computer company that sold directly to consumers, at prices lower than retail rivals could match.

By the time he was 24, the company now known as Dell (DELL, news) had revenues of $258 million. At last check, Dell's estimated net worth was $13.5 billion.

His advice for young entrepreneurs: "You've got to be passionate about it," he said in an interview with the Academy of Achievement. "I think people that look for great ideas to make money aren't nearly as successful as those who say, 'OK, what do I really love to do?

Catherine Cook

Catherine Cook, now 20, has been a millionaire for a couple of years. She and her brothers David and Geoff started myYearbook, a social-networking site popular with teens, in 2005, when Catherine and David were still in high school.

Her advice for young entrepreneurs: "Stop just thinking about it and make it happen. When you're young is the best time to start your own business, as you do not have the responsibilities you will have when you're older. The worst that can happen if you fail now is that you have firsthand experience to make your next venture a success."

Sean Belnick

Sean Belnick, now 23, became a millionaire at 16. He started selling office chairs online, an endeavor that morphed into a company called BizChair.com. Along the way, Belnick earned a bachelor's degree from Emory University's Goizueta Business School.

His advice for young entrepreneurs: "It is never too early to start. . . . There's a lot of great information on the Internet. Just do the research and find a way to do what you want to do."

Jermaine Griggs

Jermaine Griggs, now 27, became a millionaire at 23 by pursuing his passion for teaching music. His website, HearAndPlay.com, is designed to help people learn to play piano, guitar or drums by ear, without reading sheet music. More than 2 million students download online lessons each year. Griggs' plans include the launch of brick-and-mortar learning centers, a TV network and a magazine.

His advice for young entrepreneurs: "Understand the power of selling, not just things but yourself and your ideas. Study business. Study those who have come before you and find people with the same dreams and aspirations as you."

Matt Mickiewicz

Matt Mickiewicz, now 27, made his first million dollars at 22. He was instrumental in the creation of the websites SitePoint, 99designs and Flippa.com. The Internet, Mickiewicz said, gives entrepreneurs instant feedback from consumers, making it relatively inexpensive to test and launch ideas.

His advice for young entrepreneurs: "People who say it takes money to make money are using the worst excuse ever. Create massive value for others by providing a solution where no other exists."

Juliette Brindak

Twenty-one-year-old Juliette Brindak became a millionaire at 19, when the company she co-founded and runs, MissO and Friends, was valued at $15 million.

At 10, Brindak started drawing the "cool girls" cartoon figures that later became stars in her online community for tween girls. Today, she is seeking investors and preparing to take the site public as she attends classes at Washington University in St. Louis.

Her advice for young entrepreneurs: Fill your team with members who believe in your idea. "If someone starts to doubt your company and what you're doing," she said, "you need to get rid of them."

David Hauser and Siamak Taghaddos

David Hauser, now 28, and Siamak Taghaddos, 29, became millionaires four years ago. They met at Babson College and later developed the Grasshopper Virtual Phone System, designed to help entrepreneurs stay in touch with customers, investors or others while on the move. Hauser built the technology and Taghaddos took care of marketing.

Taghaddos' advice for young entrepreneurs: "Success is finding solutions in challenges that help others; money is secondary. . . . Always be on the lookout for new venture opportunities from the voids and challenges you experience in your life."

Cameron Johnson

Cameron Johnson, now 25, launched more than a dozen websites between 1998 and 2004, before he was 20 years old. He was a millionaire before he left high school.

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At age 9, Johnson started a printing company making greeting cards from his home. At 12, he made $50,000 selling his sister's Beanie Baby collection (with her permission, of course). Regarded as an entrepreneurial icon in Japan, Johnson hosted a BBC television show last year called "Beat the Boss." He now focuses on writing and guest lectures.

His advice for young entrepreneurs: "Put yourself out there. Get started, do something and start small. The lower your startup costs, the easier it is to find profitability. Create value for others, and you'll be rewarded."