The sample size was small—185 Americans with more than $25 million in net worth—but the findings are consistent with other economic research on the top 0.1 percent.

Those over 65 hold more than a third of U.S. wealth, a number that hasn't risen as quickly as the share of elderly Americans in the population, University of California Berkeley economists Emmanuel Saez and Gabriel Zucman found in a 2016 paper. In fact the very wealthiest group of Americans “is actually getting younger.”

Where is this new money coming from?

A new generation of millionaires and billionaires probably owe as much to inheritances as to self-made fortunes. “There may be more Mark Zuckerbergs at the top of the wealth distribution than in the 1960s, but also more Paris Hiltons,” Saez and Zucman wrote.

About 172,000 U.S. households have net worths of at least $25 million, Spectrem estimated last year. That's up from 84,000 in 2008.

About nine in ten investors under 38 attributed their success to “inheritance” and “family connections” in the Spectrem survey.

But the same proportion also said “hard work” and “running my own business” played a role. About 70 percent of the richest investors said they're still working.

The rise in super-wealthy young people shouldn't be all that surprising given the recent boom in Silicon Valley.

Technology and the ease of raising venture capital has created far greater numbers of new billionaires and multi-millionaires than ever before. An initial public offering or a rich funding round can mint a billionaire overnight whereas their predecessors often accumulated riches by building up empires over decades.

Adam Bowen and James Monsees, creators of the ubiquitous e-cigarette Juul, are in their early 40s and late 30s, respectively. Stanford classmates Baiju Bhatt and Vlad Tenev became billionaires at 33 and 31 last May after starting Robinhood Markets Inc., a financial services firm for millennials. And in September, a trio of cannabis-focused private equity investors in their 40s became billionaires after their bet on a Canadian pot firm surged.

Even as more young people entered the top 0.1 percent, most of their millennial and Generation X compatriots were struggling. Americans 75 and older are the only age group whose median net worth rose from 2007 to 2016, according to the Federal Reserve Survey of Consumer of Finances released in July 2018.

Typical Americans age 35 to 54 saw their wealth—heavily concentrated in housing—plunge by more than 41 percent in that time frame.

Meanwhile, the richest Americans are using complex estate planning techniques to transfer wealth to their children, grandchildren, and beyond. Ninety-one percent of investors with $25 million or more keep assets in a trust, Spectrem found, and half have three or more trusts set up.

Charity is getting less attention. Although nearly 200 of the world's richest people have signed the Giving Pledge, the Spectrem survey suggests the typical rich person is much less generous, at least so far. Of respondents with at least $25 million, just 15 percent give away $100,000 or more annually.

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