This year the world's youngest billionaires are a little older–and a lot poorer.

The world's youngest tycoons may have sprouted a few gray hairs over the last year.

Amid the global recession, the Forbes list of the World's Billionaires is smaller–and poorer–this year. As a result, the tiny club of billionaires age 40 and younger just got a whole lot smaller too.

Last year, the world's 20 youngest plutocrats were all under the age of 36. In 2009, their ages range from 25 to 40. The average age of the world's 20 youngest billionaires is 35 this year, up from last year's average of 32.

The average net worth of billionaires age 40 and under is $2.9 billion, down 30% from last year's average of $4.1 billion.

The youngest billionaire in the world is 25-year-old German Prince Albert von Thurn und Taxis, who is worth $2.1 billion. Von Thurn und Taxis first appeared on our list of the world's billionaires at age 8, but he officially inherited his family's fortune in 2001 on his 18th birthday.

He attended high school in Rome, and studied economics and theology at Edinburgh University in Scotland. The car racing bachelor's fortune fell nearly 10% after the housing crisis crushed real estate and forestry prices.

The prince regains his title as the world's youngest tycoon thanks to the economic meltdown, which pushed 24-year-old Facebook founder Mark Zuckerberg off our ranking. While Facebook is gaining millions of users each week, revenues haven't followed just yet. It's hard to imagine the privately held company being worth nearly as much as it was a year ago.

There are still a few Silicon Valley billionaires on the list of young moguls, including Google guys Sergey Brin and Larry Page, who share the distinction of being the richest billionaires under 40. Each has a $12 billion fortune.

But like the rest of us, Brin and Page have endured serious financial pain over the last year. Their fortunes have each dropped more than $6.5 billion since last March, as a sputtering advertising market pushed shares of Google down 30%.

Another tech billionaire with a dwindling fortune is former Yahoo!Chief Executive Jerry Yang. The 40-year-old, who is worth $1.1 billion these days, has lost half of his money in the past 12 months–and control of the famous search engine outfit he co-founded more than a decade ago. Yang quit as chief executive in January, after the company named Carol Bartz as his replacement.

The departure capped off a rough 2008 for the tech titan. Last February, Yang famously turned down Microsoft's $44.6 billion offer to buy Yahoo!. A few months later, billionaire Carl Icahn launched a proxy fight for control of Yahoo!'s board in an attempt to force the Microsoft sale. Icahn stopped his attack in July after Yang conceded three seats on the company's board to the activist investor. Yahoo! shares are down nearly 55% since rebuffing the original Microsoft offer

Despite the economic chaos, there is a newcomer to this year's young billionaires club: 39-year-old Sheik Mansour Bin Zayed Al Nahayan. Worth $4.9 billion, the member of Abu Dhabi's royal family stepped into the spotlight last September after buying the Manchester City soccer team for $300 million.

A month later Al Nahayan, who heads Abu Dhabi's sovereign wealth fund, swooped in to rescue British bank Barclays with a $5 billion cash investment. The young royal also serves as minister of United Arab Emirates Presidential Affairs.

A few young tycoons were able to make money this past year in the face of financial turmoil. American energy trader John Arnold added more than $1 billion to his fortune in a chaotic oil market, and Indian pharmaceuticals kings Malvinder and Shivinder Singh added $100 million to their combined net worth. - forbes

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