Not all teenage students are bad . . .
I stand by everything I wrote above. But I feel some counterpoint is in order.
There is always a danger in generalizations. Not all teenage flight students are cowboy punks. Example: In the late '80s, Oklahoma Wing CAP put on flight encampments for cadets. I was an instructor in the program one year and Project Officer for the program the next year. The program provided ten hours of flight instruction to selected cadets in the wing's 172s leading to solo. The cadets had to go before a selection board (compare to an airline interview board) and a flight screening with a CAP instructor (compare to a sim ride) to determine if they had potential. Most of them soloed.
These cadets were outstanding, motivated young people who took the program and their flying seriously. I picked up one cadet who had soloed with another instructor and finished him for his Private. He was my first signoff. I'm sure he learned a few things from me but I probably learned more by training him.
My point is not all teenage students are irresponsible. For that matter, quite a few adult students can be dangerous. Our job as instructors is to astutely separate the responsible from the irresponsible and deal with the latter group appropriately. You'll be surprised, as I was, how readily young people pick up flying. They really can be fun to instruct, and by foreclosing on young people you will foreclose on some of the joy of instructing good students. Just beware of the bad apples.