It has always, always been this way, since recorded history.
The job of a teenager is tough: they need to separate from their parents, all the while developing their own social network (because we are social animals, after all). One way to do this is to change your appearance to look dramatically different from all those "old" folks around you -- whether it makes sense or not (in fact, I suspect the less logical, the better, because that very clearly marks you as "different." At least, that's the only explanation I can think of for all the HS boys who insist on wearing shorts year-round.).
Of course, at the same time, you need to find your own social group and fit in with them. So all those "different" things tend to coalesce around some specific kinds of markers. Think, say, bell bottoms, or a Mohawk (my era, although I only went as far as a rat tail), or, yes, tattoos and piercings, or man buns, or beard-farming -- and language, as well (IMO, emojis and acronyms and other texting shortcuts are this generation's version of "groovy" and "cool, man"). And this kind of marking continues into your twenties; if you think about it, any time you move to a different environment, like college, you need to identify the local customs and expectations and figure out how to fit into your new group.
So the short version is that you don't like the way they look because you are not their target audience -- you're the old fart their instincts are telling them to distinguish themselves from. Of course, what usually happens is that kids move on into the bigger world and have to support themselves, and most realize at some point that if they want to succeed with their new peer group, they need to signal that they belong to that group, too. So they morph towards corporate clothes, adopt more "normal" hairstyles, and basically turn into you and me. :-) You're just seeing them at the beginning of that journey.
Speaking as yet another 51-yr-old woman (hi Kris!), the really fun part is when you start to see the styles cycle around, and what is "cool" is what you considered massively uncool. Like this new sideburns trend -- all I can think of is, dude, you do realize you look *just* like my dad in 1974, right?