Adults can't do it if it's severe skeletal buckteeth. They should do it before 13 years old.

If it is irregular, full of gaps, open jaws, big teeth, etc. Adults can do it without age limit. You can do orthodontics at the age of 37. Five thousand dollars for orthodontics. Search: Guiyang Nanning Guilin Orthodontics 5000 yuan lump sum price for reference.