It's hard to vote?
First, if you're black in a lot of this country, your government doesn't want you to vote. I'm not even going to mince words there. Somewhat related, look at how some states handle primary registration: if I wanted to vote in the Democratic primary for say, New York City's mayoral race this year, I needed to be appropriately registered last year. Well, what if I weren't interested last year, but I am now? Tough luck.
Second, if you're young and you have difficult work schedules you have relatively little control over, it's harder to vote. We don't vote on weekends: we vote on Tuesdays, replete with the logistical difficulties of 9-5ers battering polling stations before or after a rush commute and others working hourly or double shifts getting discouraged from voting. We're sending as many indicators as we can as a society that we don't want young adults to participate in polling stations, I think.
And voting is a habit. Almost by definition, younger people don't have it because they still need to build it. I obviously want all people to cast a vote but we might be unrealistic expecting younger voters to have the voting behaviors (or, I dare say it, the underlying institutional trust needed) of their grandparents!
