I think the answer depends on how you set up access to your app (private or public), if sign-in would be required or optional, what further restrictions might be (roles, sign-in restrictions).
Based on your description, it seems to me you would need to set up
- private access
- for 13+ users
If this is correct, then the Pro plan would suit your needs.
Do refer to Darren’s Glide Privacy Flowchart. It should help you determine what privacy settings your app will require.