Gabby will be getting her's done when she is 5 (if she wants to?).
Why? Tradition. My sisters and I were all 5 when we had ours done. It was a way of celebrating such a special age.
I reckon it's completely up to you. It doesn't hurt for long and I doubt it causes any major harm??
I had my ears peirced again when I was 15?? Something like that. I don't use the second hole anymore. They've healed up but you can still see where the hole was.
I had my nose pierced when I was 18 but took it out when I started teaching because too many children asked about it and I didn't think I was setting a good example.