Do you have to be a certain age to be in the mezzanne seating?

general admission usually covers the mezzanine, unless indicated, so any age that the ticket allows.

I was there for a rock band concert and I saw children around 8-10 years old. Also a couple with a baby in a stroller. To be able to buy alcohol, they ask for your ID before enter the building and they give you a brazalete.

I don't think age matters, as long as you are able to get your tickets for that specialized area.