I agree that terms don't have fixed meaning, but the terms still have certain essential characteristics. I'd argue that what millenials want is more accurately described as a form of hyper-individualism. It seems superficially collectivist because they want more government spending, and the GOP convinced everyone that anytime the government pays for something that's communism. But the spending is actually in service of individualism. It's directed to freeing individuals from the social obligations they would have in a more collectivist society. E.g., they want social security to free them from the obligation of caring for their parents. Then they want free child care to free them from the reciprocal obligations they would incur if they relied on their parents for childcare. They want payments for kids, so they can be freed from the obligations of marriage. They want free education, but they want to choose their course of study, not receive training in whatever jobs the government determines need to be filled in the economy.

And the reason I'm quibbling about whether you label this "individualist" or "collectivist" is that it helps explain what happens as these people get older. Why did the seeming collectivism of the baby boomers in the 1960s give rise to a period of extreme libertarian individualism in the 1980s? I think that makes more sense when you realize that what happened in the 1960s was not collectivist, but instead a surge of individualism coupled with a rejection of obligations imposed by traditional society. Viewed that way, it makes total sense how the baby boomers went on to create an economy that was characterized by the rejection of social obligation.