If no means means “all” millennials, then they should do the homework and get the numbers. Tell me how many millennials do the thing they’re talking about. Showing they’ve done the homework is credible. Lumping everyone together is not credible.
As in the comment below, if someone says “statistics show that 54% of millennials do this thing…” — that’s credible. Saying “millennials do this thing” is lazy writing and not credible.
Even worse, it’s often a screaming signal of privilege because all those “trends” they are talking about often don’t apply to the many millennials living in abject poverty, in the ghettos, in the deep south, etc.
Doing the legwork to get credible numbers is more work, yes — but it’s also more credible. In the end, it’s up to the writer if they want to trade away their credibility. Or maybe they should just say up front this is my opinion and it might not be right. That would at least be honest. :)