piercing of minors

I was writing today with a question regarding tongue piercings. I was always under the assumption that the minimum age requirement is 18. I understood it to be a sexual piercing. Lately in my area some piercers have been piercing childrens tounges as young as 14. Is the age limit a law or just a guideline? I feel it is a highly inappropriate piercing for a minor and i myself refuse to do them on anyone younger than 18. Could you please shed some light on this subject? Thank you so much for your time.