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Nearly 80 percent of millennials are not invested in the stock market, according to a new Harris poll commissioned by investing app Stash. Why? More than 40 percent said they feel they don't have enough money, 34 percent said they don't know how, while 13 percent specifically blamed student debt. The survey — which polled about 500 Americans aged 18 through 34 — also found that female millennials were especially turned off by investing. Three in 4 young women, versus 60 percent of young men, said investing was confusing. And 60 percent of millennial women said they believe the typical investor is an "old white man." About half of millennial men agreed.

Millennials' misgivings about the lack of relatable experts are not without merit, said New York City-based financial planner Douglas Boneparth. "The average age of a financial advisor is 55," he said. "There are more financial advisors over the age of 70 than there are under 30."

Yet avoiding the stock market entirely is a dangerous move for young people, who need the higher returns of riskier assets to build sustainable retirement savings.

Millennials are "missing the boat on investing," said Stash's CEO, David Ronick. Stash is start-up company pitching itself as simple solution for unsophisticated investors, allowing users to invest as little as $5 in fractions of exchange-traded fund shares. The company charges $1 a month, or 0.25 percent annually on balances higher than $5,000, though that's on top of the expense ratios of the underlying funds. (Trading app Robinhood doesn't allow for such small investments in ETFs, but is fee- and commission-free.)

These new technologies might appeal to younger investors, who are particularly conscious of expenses and transparency — and place a high premium on their free time, said Boneparth.