Age doesn't really matter...
Age does matter though. The group will be limited to the type of concepts they can do if she makes it. It would be awkward to see a 13 year old do sexy or dark concepts. She would only be able to work a certain number of hours because she's a minor, there for she would miss out a lot on group activities. Also she would look so out of place, like a little kid among a group of teenagers/women. Not saying she isn't talented, but yes, age does matter.