Sure, a bunch of them were lucky enough to inherit their wealth. China's richest woman, Yang Huiyan, owes her $7.4 billion fortune to her generous father, Yeung Kwok Keung, the media-shy chief of real estate outfit Country Garden, who transferred all his shares to her in 2005, the same year she graduated from Ohio State University.
So too Hind Hariri, 24, the daughter of the late Lebanese Prime Minister Rafik Al-Hariri. A recent graduate of the Lebanese American University in Beirut, Hariri is a fashionista who frequents Paris shows and reportedly favors designer Chanel.
But many actually made their own fortunes. The Ukraine's youngest billionaire, Kostyantin Zhevago, was only 19 when he started out as a finance director at a bank. He later gained a majority stake in its holding company. Today the 34-year-old is worth $3.4 billion and is a deputy in Ukraine's parliament.
Then there is the Chinese billionaire nicknamed Light: Xiaofeng Peng, 33, who got into solar energy in 2005 and took his company, LDK Solar (nyse: LDK - news - people ), which makes silicon wafers used in solar panels, public on NYSE Euronext (nyse: NYX - news - people ) two years later.
American John Arnold whizzed through Vanderbilt University in three years. He became an oil trader for Enron, supposedly earning the company $750 million in 2001. After the business collapsed, he started his own hedge fund, Centaurus Energy. He has done well enough to debut on Forbes' World's Billionaires list with a net worth of $1.5 billion.
The richest and most celebrated of this overachieving lot are Google (nasdaq: GOOG - news - people ) co-founders Sergey Brin and Larry Page. The pair, who are both sons of professors, met at Stanford University while pursuing Ph.D.'s in computer science and dropped out together when they were just 25 to start Google. They debuted as billionaires at ages 30 and 31. Today they are worth $18.7 billion and $18.6 billion apiece.
Still, one hopes all these hardworking billionaires take the time to enjoy their fortunes while they are young. After all, how many people in this world are lucky enough to become so fabulously wealthy before crow's feet and cellulite settle in? Larry Page seemed to take that to heart when he asked British billionaire Richard Branson, an old geezer at 57, to let him borrow Branson's private Necker Island for his wedding festivities last year; the 600-person guest list was said to include Bono and the Clintons. Earlier last year, Brin got hitched on a sandbar in the Bahamas; rumor has it that the bachelor party involved kite surfing on the coast of Greenland.
The young billionaire brat pack could learn a thing or two from dashing 24-year-old German Prince Albert von Thurn und Taxis, who is truly living a near fairy-tale existence. A billionaire since he inherited a fortune at age 18, he lives in a castle, owns 75,000 acres of woodland and spends his spare time driving race cars. Not a bad life at any age, but particularly enviable for someone who hasn't even lived a quarter of a century.