Romney actually carried the white youth vote.
The REAL issue here is DEMOGRAPHICS.
Not exactly. That’s PART of the issue, but race and sex are significant factors too. For instance, Romney might have carried the white youth vote by a hair (and I’m not even sure about that) but the margins weren’t even close to what they were with their white elders. And blacks of every age group are much more likely to vote left than their white age-mates.
So, yes, the issue is demographics, but in it’s totality — not just age.