The best age to see an orthodontist is when you first think there might be a problem with your bite.
Timing of orthodontic treatment in all bad bites makes a big difference to the ease of treatment and the results. Different bad bites are best treated at different ages but your orthodontist will advise you of the best time to treat your particular bad bite.
For young children, when the first adult teeth erupt into the mouth, or by age 7-8, if you think there might be a problem with the bite, see your dentist or an orthodontist to advise you.
For adolescents and adults the best approach to an orthodontic check-up is that sooner is always better than later.