It isn't idealism that's youthful, as demonstrated by the likes of Noam Chomsky, Jeremy Corbyn, Pete Seeger, Bernie Sanders and a lot more. It's naivete, maybe. People get more pragmatic. That can work different ways.

Sometimes getting older can mean getting more impatient rather than settling down and accepting that defeat is inevitable.

Give Hillary a strong mandate, and an effective Sandersite contingent breathing down her neck, and who knows how the flip-flops might turn out? Franklin Roosevelt had never been all that "progressive" till he found himself in a situation where radical action became realistic politics.