This depends on the nature of the orthodontic problem and the type of treatment required.
Some treatments may start around 7-8 years of age. Examples include cross bite corrections, treatment for thumb or finger sucking habits or treatment for an “underbite”.
Comprehensive treatment with braces will often be started around 11-12 years of age but this depends heavily on the developmental status of the patient. Dental development is highly variable so waiting for the eruption of all of the adult teeth is not a reliable way to best ascertain the ideal treatment timing.
There are many cases where commencing treatment prior to the loss of all of the baby teeth can make treatment simpler and sometimes avoid the need for extraction of teeth, so early consultations are advisable.