The above chart is from the Pew Research Center, and it shows the percentage of the vote going to Democrats since 1972 -- for both the under 30 age group (yellow line) and the over 30 age group (blue line). Note that President Obama virtually split the vote with his opponent in both 2008 and 2012 in the over 30 group (thanks to getting 40% of the white vote and huge majorities in all minority voting groups). But the under 30 age group was a much different story. In the under 30 group, President Obama got 66% in 2008 and 60% in 2012.
Much has been made of how the Republicans must reach out to minority groups if they want to win in the future (because white make up a smaller percentage of voters in each passing election. But they must do more than reach out to minorities. They must also address this huge deficit in the youth vote, because many believe that the party a person feels the most comfortable in as a young voter is probably the party that will stick with as they grow older. If the Republicans don't find a way to reach younger voters, they could be in for a hard time for years to come.
But the younger voters are growing up in a different world than older voters did, and they are not going to be wooed by policies that deny equal rights to any group -- whether that be minorities, women, gays/lesbians, or immigrants. These young people grew up in a much more diverse society, and they don't see their fellow citizens in the same way that older Americans do. And Republicans are not going to win any friends among the young by following policies that keep wages low or make college too expensive to attend.
In 2012, Republicans wrote off younger voters, saying they would not turn out in large numbers. They were wrong, and young voters punished them for that erroneous assumption. Thanks to the internet and social networking sites, young people are more connected to the world around them and that has raised participation rates in elections (and other political actions). This is a good thing for this country, but unless Republicans change some of their policies it will not be a good thing for them.