At what age is it generally best to start orthodontic treatment for students?

At what age is it generally best to start orthodontic treatment? My child is in 6th grade (she is my girlfriend ^^).

 

 

 

My child is currently in the 6th grade of elementary school, and I am wondering when would be the best time to start orthodontic treatment.

Some people around me say that it is okay to start after the permanent teeth have come in to some extent,

I've also heard that it's good for girls to get counseling a little earlier because of their rapid jaw growth.

Since I am still growing, I am wondering if it is better to start orthodontic treatment right away, or if I can wait until I am about a middle school student.

For those of you who have had braces done for your children in 6th grade to middle school, at what age did they start, and what tests did they undergo first? Please let me know if you have any experience :)