When my oldest son, now 21, at age ten asked me what would I do if he wanted a piercing. I said I would ask him what he wants to get done, where, and who would do it, and if after talking to me he still wanted to do it, I would not forbid him to do so but would investigate the place he wants to do it, so I can make sure they can do it safely.
Then, if Peter still wanted it, I would take him down myself, help him get it, but not pay for it. When he is done getting his piercing i would then get the exact same piercing, as a show of support for his decision.
I also said we could get t-shirts made, with our father-son photo of the occasion, and I would wear it frequently. He never brought it up again.