So my DD ages 23 came back home for 3 weeks over Christmas, her and my niece Hannah who is 18 went out for dinner and have a few drinks and decided to get some piercings done.
My DD got 3 piercings in her ear and Hannah got her nose done.
Dsis said to my DD about a week later - "By the way I'm just starting to get use to Hannah's nose piercing now"
When we saw them at Christmas as my DD was saying bye to Hannah and arranging to meet up soon my Dsis pops up and says - don't take her to get her tongue done this time 
Now my niece is not a shy or quiet person and speaks her mind so she wasn't pressured into getting it done and I doubt she would have said she was and shes 18 and therefore able to make her own choices and didn't need parental consent.