LaBella and thecolorsblend have the best responses here.
And as Not David pointed out, there is a difference between younger and older millennials. For example, I am an older millennial (b. 1982), and the youngest person I know socially is a decade younger than me (still a millennial, but younger), yet I honestly have no idea what she is talking about 99.9% of the time. And I don't think it's because she is not articulating her ideas clearly or anything...we just grew up in more different worlds than most members of previous generations probably would have, I'm going to guess because of the internet, which was not in everyone's home until I was basically an adult (I myself wasn't on the internet until I was 18, and the people I knew who were on the internet in high school were generally the tech 'nerds' and 'hackers'). So she will post things on Facebook, for instance, that are like little cartoons that show androgynous people and have text on them saying "Some women have (male genitalia), and some men have (female genitalia) -- GET OVER IT!!!", and...yeah...I mean, I was never
upset with that idea in the first place...I just plainly don't think that's how it works, so it sounds obviously wrong to me. But I guess the thinking behind such things is to be confrontational towards 'transphobes', which she probably does not realize is not some time-tested, hallowed concept that everyone with the correct politics must therefore automatically subscribe to, because it's probably been like this for most of her life, or at least for as long as she has probably been politically conscious, whereas in my case I was already well out of high school before anyone I personally knew had sex reassignment surgery, and 15+ years later that person is still the only one I know who has had it, so this idea that 'transphobia' has always been everywhere and that there's a huge number of trans people or whatever just doesn't pass the smell test...heck, I knew the person in question from back in high school, when they were just
'regular' gay!
Anyway, the point is not in this particular anecdote, but to point out that the problem among younger people is always pretty much going to be the same: that they don't really have a sense for what the world was like before them (this is not always the case, of course; plenty of people have aunts, grandparents, etc. they can talk to), and when this is combined with the naturally skeptical outlook of many youth who are still trying to figure the world out or their place within it, it's going to present a challenge to anyone who is coming to them with a message that is presented as (or supposed to be) timeless, based on a non-shifting morality, etc (however you want to characterize Christianity). If the millennials or Gen Z are unique in any way, it is that the advancement of technology has made the pace of change so much quicker than it would've been in earlier times, such that 'generations' in the sense of a group of people bound by an age cohort and an assumed background of shared experiences seem to be getting shorter and shorter. I can't relate to my 27/28 year old friend as well as I can to my 30-40 year old friends and family, but I'm not entirely sure that any random friend I could pick out who is in their early 30s could relate to the average person in their late 20s now, either, to say nothing of someone in their early 20s (because I don't personally know anyone in that age group to begin with).
So...things are accelerating, and it's harder and harder to keep up, not even with what's 'hip' in a youth culture sense, but even with what people are trying to say. (Typical 'old person' reply, right? Hahaha. It's true, though!)