Billion-dollar birthday

NEW YORK — He famously wears a hoodie, jeans and sneakers, and he was born the year Apple introduced the Macintosh. But Mark Zuckerberg is no boy-CEO.

Facebook’s chief executive turned 28 on Monday, setting in motion the social network’s biggest week ever. The company is expected to start selling stock to the public for the first time and begin trading on the Nasdaq Stock Market on Friday. The IPO could value Facebook at nearly $100 billion, making it worth more than such iconic companies as Disney, Ford and Kraft Foods.

At 28, Zuckerberg is exactly half the age of the average S&P 500 CEO, according to executive search firm Spencer Stuart. With eight years on the job, he’s logged more time as leader than the average CEO, whose tenure is a little more than seven years, according to Spencer Stuart.

Even so, the pressures of running a public company will undoubtedly take some getting used to. Once Facebook begins selling stock, Zuckerberg will be expected to please a host of new stakeholders, including Wall Street investment firms, hedge funds and pension funds who will pressure him to keep the company growing.

Young as he may seem — especially in that hooded sweatshirt — Zuckerberg will be about the same age as Michael Dell and older than Steve Jobs when those two took their companies, Dell Inc. and Apple Inc., public. In his years as Facebook’s CEO he’s met world leaders, rode a bull in Vietnam while on vacation, started learning Mandarin Chinese and as a personal challenge, wore a tie for the better part of a year.

Facebook, of course, got its start in Zuckerberg’s messy Harvard dorm room in early 2004. Known as Thefacebook.com in those days, the site was created to help Harvard students — and later other college students — connect with one another online. The scrappy website later grew to include high-schoolers, then anyone else with an Internet connection. Today more than 900 million people log in at least once a month, making Facebook the world’s definitive social network.

All along, Zuckerberg has shown a maturity beyond his years. As the site grew rapidly and caught the eye of big media and rival Internet companies, Zuckerberg consistently rebuffed mouthwatering buyout offers, including those from Google Inc. and Yahoo Inc.

“Simply put: we don’t build services to make money; we make money to build better services,” Zuckerberg wrote in his letter to prospective shareholders. “And we think this is a good way to build something. These days I think more and more people want to use services from companies that believe in something beyond simply maximizing profits.”

People who’ve observed Zuckerberg closely say his age is an asset. His is the generation that grew up with social networking, with computers all around them and the Internet as something that’s always existed. Many of his employees are younger than him, as are a lot of the up-and-coming technology entrepreneurs with whom he competes.

“I don’t think you could build a company like this if you were an old guy like me,” says David Kirkpatrick, a 59-year-old author who chronicled the company’s early history in “The Facebook Effect.”

Kirkpatrick first met Zuckerberg six years ago. He says he was impressed with his vision, even then.

“It’s the willingness to take risks, the willingness to abide by a very contemporary vision … I don’t think that he’s too young. I think most CEOs are too old.”

Zuckerberg, who lives in Palo Alto, Calif. with his girlfriend and a white Hungarian Puli dog named Beast, has matured as a leader with the help of experienced mentors.

Rebecca Lieb, analyst at the Altimeter Group, says Zuckerberg has assembled a team of “truly exceptional lieutenants.” David Ebersman, Facebook’s chief financial officer, who hails from biotech firm Genentech, is another example. Zuckerberg hired him in 2009, saying that Ebersman’s previous job, helping to scale the finance organization of the fast-growing biotech company “will be important to Facebook.”

He was right. Facebook’s revenue grew from $777 million in 2009 to $3.7 billion last year.