I'm another that believes in doing it when the child asks and is old enough to look after them. DD had hers done when she was 7, to my disgust X-MIL had them done at the hairdresser with a gun when I was planning to take her to a proper piercer, and sure enough they got infected for a couple of weeks. She eventually let them close up and doesn't have them anymore. I'll think about it if she asks again but she'll get them done properly or not at all.

I had mine done the first time at 5, let them close up and then again after I left school - the private school I went to didn't allow earrings at school. Which is an entire other can of worms worth thinking about in relation to this discussion