"Trends in the opinions of America's youngest voters are often a barometer of shifting political winds. And that appears to be the case in 2008. The current generation of young voters, who came of age during the George W. Bush years, is leading the way in giving the Democrats a wide advantage in party identification, just as the previous generation of young people who grew up in the Reagan years -- Generation X -- fueled the Republican surge of the mid-1990's.
"In surveys conducted between October 2007 and March 2008, 58% of voters under age 30 identified or leaned toward the Democratic Party, compared with 33% who identified or leaned toward the GOP. The Democratic Party's current lead in party identification among young voters has more than doubled since the 2004 campaign, from 11 points to 25 points."
http://pewresearch.org/pubs/813/gen-dems