The 14 youngest billionaires on The Forbes 400 make up just 3.5 percent of list.
Nine of these 14 folks under 40 are tech entrepreneurs; the rest inherited their fortunes.
The youngest member of The Forbes 400 for the second year in a row is 26-year-old Snap Inc. (formerly Snapchat) CEO Evan Spiegel.
The richest member of the under-40′s is also the fourth richest person in the country: 32-year-old Facebook CEO Mark Zuckerberg with a fortune of $55.5 billion.
32-year-old Dustin Moskovitz, who cofounded Facebook with Zuckerberg, and Napster cofounder Sean Parker, 36, who was an early Facebook investor and briefly president of the company, also made the list.
Airbnb cofounders Brian Chesky, 35, Joe Gebbia, 35, and Nathan Blecharczyk, 33, made the list.
Ubiquiti Networks founder Robert Pera, 38, who got his start at Apple in 2003 but struck out on his own two years later earned a spot as well.
The only newcomer under the age of 40 is Walmart heir Lukas Walton.
