I think one aspect of the criteria should be that the child should be able to spell Katy Perry's name correctly.
All joking aside, I think it depends on the parent, and what they are comfortable with exposing their child to. Katy does confront some mature themes through her music and concerts, swears occasionally, discusses the female/male anatomy, etc, so If you are comfortable exposing your child to such LEWD (
) behavior, then I see no reason to put an age bracket on any concert goer. That being said, if it is a young child, as in under the age of 14, I wouldn't suggest general admission or any type of no seating area as the child is apt to either get lost or trampled. Older fans can be vicious in GA.