I'm 13, I've wanted my belly button pierced since I was about 10, mum has always said no, but I think I've persuaded her, I am quite developed for my age but I'm worrying about the hole stretching as I grow? Also, how long is it after having this piercing that you can go swimming again?

Yes, as long as you go to a clean and sterile shop. One that has all the right certifications and licenses. Find a shop and even call the heath department in your area and ask about them if you'd like. I have had many piercings, never had a problem going to a clean and certified facility. Never go to one just because it's cheaper.

Yes why no.