Millennial investors are driving the ETF trend.

Millennial investors are driving the ETF trend. U.S. exchange-traded funds took off around 2000, and now have a value of more than $2.2 trillion in assets. According to insight from Schwab's 2016 ETF Investor Survey, 35.8% is the average ETF allocation in the average Millennials’ portfolio and 60% say that they “expect ETFs will be the primary investment vehicle for their portfolio in the future”—while only 38% of Gen X and 19% of Boomer investors agreed with that statement. Lower costs are most likely what is drawing in younger investors. (CNBC)