What is the legal age for nose piercing with a parental consent?

Once you have parental consent there isn't a specific age. Although you might want to check with your principal (if you go to school) to see if you're allowed to have one. I'm in middle school and people have all sorts of piercings. I guess it just depends on the authority in your school and you being comfortable with it. A nose piercing is a simple sort of piercing, so you should be fine.