I've been a secondary school teacher for over 30 years....and for all of that time and in my own teenage years the media periodically points the finger at a minority of teenagers and gets quite jingoistic about them and fails entirely to notice that 95% of teenagers are normally well behaved and not indulging in gang warfare at all.It certainly peed me off when I was a teenager in the 60's and 70's.
In fact if you go back far enough I'm sure you'll find all sorts of newspaper reports of gangs back into Edwardian and Victorian era and even further back still than that.
Adults screw the world up and then complain about the young....Typical.