I think my generation, which was people born around 1980, started to fall out of the interests of the government. It became more about pop culture for us , not what the government was doing. I really didn't start paying attention until i hit my mid 20's. It was then I realized how important it was to vote.
The political parties in the United States are failing to engage those who are young. But they are also failing to engage those who are middle aged and old! They have become to many of us necessary but irrelevant and filled with people who seek first their own power and gain.
No, the political parties of today are not failing to engage young people, what is happening todays is that the young people have a lot different views and ideas than their parents did, and than their grandparents did, so the politicians need to change their ideals so that they get young votes.
If anything, of late, I have seen political parties really scrambling to get young people to pay attention to them. Even the Republicans are starting to try to rally young people, instead of relying on their aging base who is starting to wear thin. Political parties have to do this.
The democratic party is currently very successful at engaging young people when compared to the Republican Party. This may be due to the Democrats having a message of future, hope, and healing as opposed to the Republican Parties message of profits, low taxes, and less government. The two messages speak differently to different generations. The young just don't really care about taxes.