The best story I ever heard about this was a single dad who had to take his teenage daughter to the doctor because she got an infection from inserting a toothbrush handle or something else that wasn’t sanitary, and instead of giving her ANY kind of scolding or negative judgement, he was very loving and helped her laugh it off, and then he just left on her pillow a $100 gift card to Adam & Eve or some other large, commercial, adult site that lets you buy gift cards.

I don’t think it’s appropriate to even suggest an age here, but I think as a parent you will know when it’s time to have the talk/leave the card.