Gallup has some fascinating data out, based on more than 120,000 interviews they've completed over the past four months, on the way that partisan identification breaks down by age:
Democrats, somewhat unsurprisingly, have the largest partisan ID advantage among Gen Y'ers, followed by among Baby Boomers. Republicans do relatively well (although are still at a net disadvantage) among Generation X'ers.
What's interesting, though, is what happens when we look at not these abstract generational categories, but rather at the following question: who was President when you turned 18? As annotated in the chart below, the popularity -- or lack thereof -- of the President when the voter turned 18 would seem to have a lot of explanatory power for how their politics turned out later on:
Partisan ID Gap, Based on Identity of President When Voter Turned 18
It's become common knowledge that the younger generation is highly predisposed toward Democrats. (Actually, that's not quite right -- they're more predisposed against Republicans than they are toward Democrats -- but the net effects on their voting behavior are probably about the same.) What's more remarkable, though, is how sharp the increase in the partisan ID gap becomes at about age 25. People aged 26-34 are pretty Democratic, put people aged 18-25 are really Democratic.
http://www.fivethirtyeight.com/2009/05/bush-may-haunt-republicans-for.html
