Only 72 percent of voters in the 2012 election were non-Hispanic white--the smallest percentage ever recorded by exit polls.
The detailed demographics of 2012 voters (such as the non-Hispanic white share of voters by age) will have to await Current Population Survey results. Following presidential and congressional elections, the Current Population Survey asks Americans whether they voted, producing detailed profiles of voters by demographic characteristic--including age-by-race-and-Hispanic-origin crosstabs. It will take until next year before we get those results.
We don't have to wait until next year to conclude that this election was all about the demographics. NBC News summed it up: "What happened last night was a demographic time bomb."