You have it backwards. The age gap is because of race. Not vice versa.
Partially true although amongst whites 18-29 it was a lot closer than amongst older whites never mind I suspect Romney's huge majority amongst whites 18-29 in the South probably skewed the results somewhat too. Lets remember in the New England states and Pacific Northwest or even Upper Midwest which are fairly white, Obama did much better amongst younger voters than older ones. Off course this is not unique to the US. In Europe, Canada, Australia, and New Zealand, parties on the left tend to do better amongst younger voters than older voters. In the 2005 British election, the Conservatives came in third at under 20% amongst the under 30 crowd while won the over 50 crowd. Likewise here in Canada, the NDP (left wing party) won the under 30 vote while the Conservatives got close to 50% amongst the over 65 crowd. People tend to be more idealistic when young while get pragmatic and also more resistent to change as they get older. Also the marriage gap may be a reason too since amongst married men vs. married women, there wasn't much difference, whereas amongst unmarried women; Obama did significantly better than unmarried men although he won both and those groups would be highest amongst the young and the old.
But if you flip the question around, black voters over 65 were actually slightly MORE likely to vote for Obama (91-6) than black voters under 30 (93-8). So being old per se doesn't make you more likely to vote Republican. Being old and white does. To some extent, being old and Hispanic does, in that Romney "only" lost Hispanics over 65 by 30 points, where he lost Hispanics under 30 by 50 points, but clearly even if the average Hispanic was as old as the average white person Obama would still have won Hispanics by a huge margin.
