I haven't really dug through it, but there is an interesting graph in here: Young-Adult Voting: An Analysis of Presidential Elections, 1964–2012 https://www.census.gov/prod/2014pubs/p20-573.pdf In '76, the oldest fuckers began their upswing in voter participation. They're the only age group where participation isn't trending downwards.
There's a number of interesting graphs in there, actually. The one that pretty much indicates the youth vote is driven by inspiration (first term Clinton, '92, first term Obama, '08) is one. The one that indicates the female vote under 30 has gone down while the female vote 30-44 has gone up is another. I'd say the first graph is about engagement. I'd say the second graph is about this: "won't anybody think of the children?"