I've noticed this a lot on public transport, trams particularly from teenagers say 15, 16 years old or thereabouts. And in town.
They seem far more childish than my friends and I were at the same age. We were wanting to be seen as grown up. Now I see a lot of squealing, shouting, shoving and pushing, yelling and behaviour I'd expect in seven year olds. Usually in mixed groups, but not always.
I was mortified if I was seen as a "child" at 15 (technically I was of course) and we were just not like this. I'd have been mortified if I'd acted like this.
Have today's young people really changed so much? I'm talking late 90s here not the 1960s!