I am sorry that you are having difficulty with not being able to register your child online due to their age.
Please verify that the form you are using to register your child is for new students for the 2024-2025 school year. It is possible the school does not have the form ready for next school year's enrollments.
I have included this KB article to assist with troubleshooting Adding Students. If you still need assistance with the school year for the form, I recommend reaching out to the school district's registration department or the campus.