18-24 in 2016 is very different than 18-29 in 2015. Those 2015 23-29 year olds are far, far more liberal than the 2015 17-22 year olds. 1992 serves as a breaking point between a more liberal and a more centrist (or, really, more evenly polarized) generation.
Do you have a source for those claims?
I doubt it. I have a source though:
http://www.cnn.com/election/2014/results/race/house#exit-polls
18-24: 54% Democrat 44% Republican 2% Other/NA
25-29: 54% Democrat 43% Republican 3% Other/NA
Not really much of a statistical difference.
Plus, that's a recent midterm, when many of the most liberal folks just stayed home.
Just because there's low turnout and Democrats get crushed does not NECESSARILY mean that liberals are staying home. Midterms are always going to be lower turnout, and Democrats win some of them, too.