This graph from the Pew Research Center is one of the most interesting I have seen in awhile. It shows that in 2004 Democrats started developing a modest edge with young voters but in 2008 under Obama that youth advantage exploded and Obama, for the most part, has managed to hold onto that edge so far this cycle. From Pew:
Not since 1972 has generation played such a significant role in voter preferences as it has in recent elections. Younger people have voted substantially more Democratic in each election since 2004, while older voters have cast more ballots for Republican candidates in each election since 2006. A new Pew Research Center study suggests this pattern may well continue in 2012. Millennial voters are inclined to back President Barack Obama by a wide margin in a potential matchup against former Massachusetts Governor Mitt Romney, while Silent generation voters are solidly behind Romney. Baby Boomers and Generation X voters, who are the most anxious about the uncertain economic times, are on the fence about a second term for Obama.
This new strong Democratic preference among young voters is why in the past few years we have seen state Republican parties make very aggressive pushes for more restrictive voting rules in the name of stopping “voter fraud.” In the past two years the GOP has passed new laws in Wisconsin, Maine, Kansas, and Florida that will make it harder for young adults to vote. The GOP has also tried but failed to pass similar laws in several other states. The laws often impede young college age adults who tend to move much more often so they don’t always have a current state-based IDs and need to re-register often. Back in the 90’s having election laws that made it marginally easier for young college age people to register and vote had only a relatively small impact on elections, but with this huge partisan age gap any real increase or decrease in youth turnout can have a significant impact.