intro: Mark Zuckerberg, CEO of Facebook, turned 28 on Monday, just four days before his company is expected to have the biggest tech IPO ever, now with an expected value of over $100 billion. Zuckerberg holds many other records for his age. Forbes lists him as the second youngest self-made billionaire in the world -- eight days older than Dustin Moskovitz, a fellow founder of Facebook. Zuckerberg is the youngest CEO of a Fortune 1000 company to go public.

According to the digital marketing firm eMarketer, Facebook is estimated to have global revenue of $6.1 billion in 2012, which would allow the company to join the Fortune 500. Zuckerberg would be the youngest CEO to lead a company on the list of current Fortune 1000 companies, according to the recruitment firm Korn/Ferry International.

BoardEx, self-described as a "Relationship Capital Management" solution, compiled a list of CEOs running Fortune 500 companies, ranked by age.

Before Zuckerberg officially joins the list, here are the nine youngest CEOs leading large U.S. companies:

quicklist: category: Age 39 title: Lawrence (Larry) Edward Page media: 16344251 text:

Larry Page, CEO of the search giant Google, is the youngest chief executive officer, and the only one under age 40, currently running one of the 500 biggest U.S. companies by revenue.

Page, who co-founded Google with Sergey Brin and was formerly its president of products, has only held the role of CEO since April 2011, when he took the reins from Eric Schmidt, now executive chairman.

In 1998, Page and Brin started Google while they were students at Stanford University.

Neither completed their Ph.D. studies after they found success with the search engine and advertising behemoth, which had revenue of $37.9 billion in 2011 and was ranked No. 73 on the Fortune 500 list.

quicklist: category: Age 42 title: William J. Lynch Jr. media: 16345252 text:

Barnes & Noble Inc. CEO William Lynch Jr., 42, began running the book retailer in March 2010. He was previously president of the company's e-commerce operations. Before that he managed HSN.com and was CEO of Gifts.com. With plenty of digital experience under his belt, Lynch is pushing Barnes & Noble's e-reader, the Nook, to compete against Amazon's Kindle and Apple's iPad. Last month, Microsoft took an 18 percent stake in the Nook unit, now worth $1.7 billion.

Barnes & Noble had revenue of $7.0 billion in 2011 and was most recently ranked No. 360 in the Fortune 500 list.

Lynch studied economics at the University of Texas at Austin and received an MBA from the Columbia School of Business, according to his company biography.

quicklist: category: Age 42 title: David T. Blair media: 16350058 text:

The healthcare company,, Catalyst Health Solutions Inc. had revenue of $5.3 billion in 2011 as a prescription drug and pharmacy benefit manager with CEO David Blair at its helm. Blair, 42, joined the company as CFO in 1997 and was named CEO two years later.

Blair's father, Thomas Blair, co-founded Catalyst in 1998 before it went public in 1999. Thomas Blair retired from the board of directors in December 2008.

Catalyst Health Solutions Inc. is ranked No. 455 on the Fortune 500 list.

quicklist: category: Age 43 title: Heather M. Bresch media: 16345913 text:

Heather Bresch, CEO of Mylan Inc., is the only woman among the young CEOs on this list. Bresch, 43, has had a 20-year career at Mylan, self-described as one of the largest generic and specialty pharmaceutical companies in the world. She was previously Mylan's president, chief operating officer and chief integration officer.

She has also led the Generic Pharmaceutical Association and received her undergraduate degree from West Virginia University, according to Mylan's website.

Mylan is No. 396 on the Fortune 500 list with revenues in 2011 of $6.1 billion.

quicklist: category: Age 44 title: Francisco D'Souza media: 16345240 text:

Francisco D'Souza, 44, is CEO of Cognizant Technology Solutions Corp, an information technology services company based in Teaneck, N.J.

D'Souza joined Cognizant as co-founder in 1994, the year it was launched as a division of Dun & Bradstreet Corp., the business information provider.

D'Souza received his undergraduate degree from the University of East Asia in Japan and an MBA from Carnegie-Mellon University.

Cognizant is No. 398 on Fortune's 500 list with revenues in 2011 of $6.1 billion.

quicklist: category: Age 45 title: Theodore (Ted) A. Mathas media: 16345299 text:

Ted Mathas became chief executive officer of New York Life Insurance Co. in 2008 after he became president in July 2007. He became chairman of the board in February 2009, when he was just 41.

Now 45, Mathas has been a director of the company since July 2006 when he became chief operating officer. He joined the company in June 1995 as an officer in the asset management department, according to the company website.

Mathas graduated from Stanford University in 1989 and received a law degree from the University of Virginia in 1992.

The company is No. 86 on the Fortune 500 list with revenues of $34.4 billion.

quicklist: category: Age 45 title: Marc N. Casper media:16345195 text:

Marc Casper, 45. is president and CEO of the scientific instrument and research company ThermoFisher Scientific, based in Waltham, Mass. The company has 39,000 employees; it reported revenues of $11.8 billion in 2011.

Before joining the company in December 2001 as president, he was CEO of Kendro Laboratory Products, which was acquired by Thermo Electron in 2005.

Casper has degrees from Wesleyan University and the Harvard Business School.

ThermoFisher Scientific is ranked No. 225 on the Fortune 500 list.

quicklist: category: Age 45 title: Alec R. Cunningham media: 16350849 text:

WellCare Health Plans Inc. CEO Alec Cunningham, 45, has led the company since December 2009. He joined the company's executive team in 2005 as vice president of business development, according to the firm. Based in Tampa, Fla., WellCare provides insurance and managed care services.

The company is ranked No. 401 on the Fortune 500 list with revenues in 2011 of $6.1 billion.

quicklist: category: Age 46 title: Michael Rapino media: 16345373 text:

Michael Rapino, 46, is CEO of Live Nation Entertainment Inc., the mega-events company based in Beverly Hills. Live Nation merged with Ticketmaster.

Self-described as the "leading live entertainment and eCommerce company," Live Nation produces over 20,000 shows for more than 2,000 artists globally.

Rapino became president and CEO of Live Nation Entertainment in 2010, before which he was president and CEO of Live Nation since August 2005.

Rapino has a degree in business from Lakehead University.

Live Nation Entertainment ranks No. 450 on the Fortune 500 list with revenues of $5.4 billion in 2011.