Players of any age can sign up to use the app however if you are under age you will need permission from your guardian, who is in control of your Apple ID with Apple Family Sharing.
With Family Sharing, you can create Apple IDs for children under 13. Apple IDs allow them to participate in Family Sharing and use other Apple services such as iCloud, iMessage, FaceTime, and Game Center.
To participate in Family Sharing, all family members must have their own Apple ID. Children under 13* can't create an Apple ID on their own. However, as a parent or legal guardian, the family organizer can provide verified parental consent for a child to have their own Apple ID, then create it on the child’s behalf. If your child already has an Apple ID, you can update their email address, date of birth, security questions, and more.
When you create an Apple ID for a child, it will be added to your family group automatically.
For more information about Apple Family Sharing, please visit https://www.apple.com/family-sharing/