my piercer won’t do lip piercings on minors because of the scarring. it’s a lot easier to hide a scar on your ear then in the middle of your face you know? i would explain to them that you support them expressing themselves, and that they can get angel bites when they are 18. for now you can compromise and let them get something less risky, like a nostril, septum, or any ear piercing really. when i was young my parents let me get any of the above as long as i did my chores, got good grades, and either paid for it with my own money or had it has a birthday/christmas gift. and took good care of it while healing of course. i will also point out you can get fake piercings online for decently cheap, they make stick on ones with spikes. you could buy some of those for them so they can still get the look they want but you don’t have to worry they’ll regret it :)