Forbes has listed the 400 richest Americans in its Forbes 400 list. On that list were 20 billionaires under the age of 45. Here are the top 10 youngest billionaires in the United States.

1. Dustin Moskovitz, 29, helped Mark Zuckerberg start Facebook (FB). He has a net worth of $5.2 billion.
2. Mark Zuckerberg,  29, is only eight days older than Moskovitz. He has a net worth of $19 billion.
3. Scott Duncan, 30, is one of four heirs to Enterprise Products Partners (EPD). He has a net worth of $5.5 billion.
4. Sean Parker, 33, is the founder of Napster and the current director for Spotify. He has a net worth of $2 billion.
5. Robert Pera, 35, is the founder of Ubiquiti Networks (UBNT) and use to be an engineer for Apple (AAPL). He has a net worth of $1.95 billion.
6. Jack Dorsey, 36, co-founded Twitter and has a large stake in the startup Square, which allows devices to process credit and debit card payments. He has a net worth of $1.3 billion.
7. Nick Woodman, 38, is the founder of Woodman Labs, makers of GoPro cameras, which are used in outdoor activities. He has a net worth of $1.3 billion.
8. Chase Coleman, 38, is the co-founder and manager of the Tiger Global hedge fund. He has a net worth of $1.4 billion.
9. John Arnold, 39, made a career out of hedge funds in 2012 at age 38. He has a net worth of $2.8 billion.
10. Sergey Brin, 40, is the co-founder of Google (GOOG) and now manages the company’s Google X division. He has a net worth of $24.9 billion.

To see the other 10 youngest billionaires click here.

Bill Gates took the top position in Forbes 400 list for the 20th year in a row with a net worth of $72 billion