There are a lot of 16/17 year olds there. You can't buy alcohol inside the arena unless you have an 18+ wristband, and you need proof of age for that. You can't take alcohol from the campsite into the arena. So the amount of drinking depends on whether your child or their friends can buy much outside to take into the campsite. Also depends on how into the music your child is, or whether they would be mostly going for the social experience!
The campsites further away from the arena are the quieter, more civilised ones. Last year I did a bit of salvage afterwards at one of camping fields nearest the arena, and it was truly disgusting - looked as if no one took anything home with them.
My dd has been for the last 2 years, but just for each day (she was 14 and 15, June birthday), and she's going again this year. Last year she said she was going to camp this year, but over the year she's decided to come home each night again - helpfully, she is going with a friend whose parents didn't want her to camp! We are close enough that it's probably quicker to walk back to ours than to the further away campsites that she would have wanted to stay in
I would have let her camp, but I'm glad she's not.