Touchy sometimes.
I have worked on cases as young as 4 years. Need of a quadhelix.
Starting time might be early for a case that has special needs. Cleft palate and such.
Some Drs. won't do what is refered to as "first phase" or some such thing. Others will work on super youngsters sometimes because the parents are insistant, and money is no object. The reasons for an early start are numerous.
My son did not require ortho. Walks funny, but, so do I. I haven't had ortho either.
Seems to be most cases I have seen over 38 years are most cosmetic in nature. Then again, what do I really know, xrays show a problem I can't see on work models.Also a perfect alignment is thought to be cleaner and such. Shark like is difficult to floss.
I saw it posted just recently in my forum on another site, "Start slow and build up, only floss the teeth you want to keep"
My opinion is nothing more than that, and I am an expert on my opinion.
Seems maybe the teen years are a good start point for the most part, to me.
Having a mouth full of brackets is a statis symbol as well for some teens. Some till the discomfort sets in. (There is no such thing as pain in ortho, just discomfort.)