Ezra has a perceptive op-ed on the Obama McCain age gap:
The real significance of the age difference is not about health and mortality but about worldview, about ideology, about how the candidates understand the threats we face and the world we're in. A candidate like McCain, born in the final years of the Depression and shortly before the outbreak of World War II, will simply have a different frame of reference from a candidate born, as Obama was, in 1961, the year President Kennedy took office and Bob Dylan arrived in New York. And that should be discussed openly.
It is one of those things that doesn't fully emerge until the two candidates are placed next to one another. But I have a feeling that the generational narrative of this campaign from here on out will be a very powerful one. It isn't that one man is much younger than the other. It is that his supporters are skewed younger as well - and that the issues in this campaign resonate differently with the generations.
The culture war means less as the age cohort gets younger; the reflexive assumption that America is required to be everywhere on the planet, with 50 planned permanent military bases in Iraq, for example, is less obvious to a post-Iraq generation than to those with memories of World War II; rising debt will worry the next generation more than those on the brink of retirement; social questions such as same-sex marriage are no longer very salient questions for those under 40.
My own sense is that this will be the defining faultline of the contest. Not age as such; but generation. And the key voters will be those in between and whether they decide to ally themselves with their parents or their children.