Facebook founder and CEO Mark Zuckerberg turned 28 on Monday, and his true birthday present will arrive on Friday when the social networking site sells stock and begins trading on the Nasdaq. But he's not the only young gun out there.

By nearly every significant measure, the talismanic Harvard dropout is breaking the mold. He's the world's youngest billionaire, and 14th richest American, according to Forbes.

Zuckerberg is already miles ahead of his brethren in the tech realm, whose heavy hitters were still climbing towards success at the tender age of 28. Bill Gates' Microsoft did not release the first working version of Windows until he was 30, and it was another decade before cheap computers and Windows 95 merged to make Microsoft and the Harvard dropout a household name.

Apple founder Steve Jobs' 28th year was marked by the fateful decision to recruit John Sculley from Pepsi-Cola to serve as Apple's CEO -- a choice that eventually led to Jobs' ouster from the company he founded.

Google co-founders Sergey Brin and Larry Page are closest to Zuckerberg's precocity, with their search-engine megalith already an established entity in the online world. But its IPO (and the ensuing riches) didn't come until the duo's 31st birthdays.

Not to mention Zuckerberg has more followers on Google's social network Google+ than the search engine's founders.

But is the color-blind founder of the world's largest social network a model for precocious young entrepreneurs or the first in a long line of wet-behind-the-ears executives on the horizon?

Here are five CEOs younger than Zuckerberg, whom you may be calling your boss one day:

Harli Jordean, 9, Marble King



Harli Jordean has built an entire business around his love of marbles.

The unofficial world record holder for World's Youngest CEO presides over the U.K.'s Marble King, a site dedicated to his personal obsession.

The 9-year-old London boy's devotion to marbles started at the age of 6, but within two years he grew frustrated by the lack a selection. Enter Marble King, a Web site suited for his very particular interest and whoever else has an obsession with marbles.

It's been more than a year, and the kid has established himself as the main branding device of his fledgling company, has a Twitter account (which we hope is tightly monitored by his mom) and is setting up franchises! He even has set of marbles he's peddling for $1,000. Jordean is on the verge of a marble empire.

What was Zuckerberg doing at that age? Learning Atari BASIC Programming?

Sindhuja Rajaraman, 14, Seppan


Already a world record holder for animation, Sindhuja Rajaraman also skips class to keep her company running.

This 14-year-old CEO of Seppan, a Chennai, India-based animation company, heads a team of 10 people so far and conducts business with the air of a seasoned professional.

Though my teammates are older they always take my assistance and, in turn, they also guide me, she told the Economic Times. They have taught me what corporate world is and what team management is. In fact, I draw a lower salary than them.

The fledgling corporate leader has already earned a Guiness Book World Record in fastest animation. And she has sacrificed school work and classmates to focus on her company.

My school has given me an exemption, she said. I go for tuitions after work and go to school to write my exams alone. One needs to sacrifice certain things to chase dreams.

What was Zuckerberg up to at 14 years old? Fencing?

Adam Goldstein, 24, Hipmunk


Adam Goldstein, founder of travel site Hipmunk.com.

Sure, Facebook was already a known entity when Zuckerberg was 24, but Adam Goldstein has the same hacker credentials and is the co-founder of now-defunct BookTour and travel site hipmunk.com.

The 2010 MIT grad holds degrees in electrical engineering/computer science and mechanical engineering, and was North American debating champion in 2010.

Jared Hecht, 24, GroupMe


Jared Hecht, founder and subsequent seller of GroupMe.

Hecht along with partner Steve Martocci founded group-texting service GroupMe, which gives a single phone number to a collective of people. Unlike Zuckerberg, Hecht cashed out and sold his company to Skype for $85 million.

David Karp, 26, Tumblr



David Karp, founder and CEO of Tumblr.

How do you top Facebook? Some would argue Twitter. How do you top Twitter? Ah, therein lies Tumblr -- a pseudo-twitter with a little bit more room to play.

Karp founded the site as a liberation from the then-rote norms of blogging or tweeting, something much more free-form, much less verbose.

Karp even took potshots at Zuckerberg's company, calling it out for constricting creative expression. Nobody is proud of their identity on Facebook. Ouch.