CBS News has the story The young voter turnout in 2014. Near the beginning it says:
Voters ages 18-29, a core part of the Democratic party’s coalition, made up 13 percent of the national electorate this year, compared to 19 percent in 2012, representing approximately 14 million fewer young voters–an early estimate based on exit polling and the number of votes cast for the House of Representatives.
Then it goes on to give you lots more fascinating pieces of data. Remember that as Nassim Nicholas Taleb said in his book The Black Swan, and here I paraphrase, people run into trouble not so much in telling what happened historically, but they run into trouble when they try to tell you why.
Nevertheless, I have been raving on about why it happened ever since the election. So trust me, folks, I am an exception to what Taleb said. 🙂