I look at a great number of posts from hosts who are reluctant to give negative reviews, @David64 so I hope you will give a thumbs down review to these guests. Air BNB is promoting Instant Booking and the only way for hosts to be "safe" is if other hosts will provide honest reviews.
I don't know if there is a "trend" about "younger" guests, but I do understand the popularity of Air BNB has increased with all the marketing so the odds of getting a guest that just doesn't get is increased.
I think people who would have booked at Motel 6, think they can get better accommodations through Air BNB, which they can, but they have a Motel 6 mentality. Sorry Motel 6, but price driven bookings are often disappointing to the host who is just trying to offer a good value to respectful people. Maybe you should raise your rate!