Exchange-traded funds make up roughly 10% of the average Generation X or Y investment portfolio, according to  data from TD Ameritrade, and people of all ages have higher ETF balances today than six months ago. 
And they’re not just using ETFs more often; they’re using them in more sophisticated ways.

“Retail investors are really embracing the exposure to more specialized markets that ETFs can provide,” said Mike McGrath, director of ETFs, TD Ameritrade. 
Eighteen months ago, about 47% of all ETF shares were in U.S. stocks. Today, that share is roughly 51%, while other sectors have seen proportional losses.  Holdings in international stock ETFs fell from 18% to 17%, taxable bonds from 11% to 10%, and alternative investments from 12% to 7%. Commodity ETFs have grown more popular, rising to 14% from 11%.