J.J.
For me, the key was to go to an orthodontist I can trust. I waited until my son was 14 before starting orthodontia, because his baby teeth never fell out. He ended up having 9 baby teeth extracted and then started orthodontia.
I have wondered if it might have been less of a production if he had started earlier. Now I realize that we probably didn't have to wait for the baby teeth to fall out. So it might have been better to start sooner.
BUT my biggest concern about starting an 8 year old is that it's a huge amount of pressure on a child, to keep track of the brace, because it will most likely be removeable. If they lose it, it costs at least $100 to replace.
This is just my opinion, but I think this should be a big concern, whether the child is mature enough. And make sure you have an orthodontist that can answer every question you have, including "what can we anticipate if we don't go this route." I had several consultations with the orthodontist before we signed a contract and started paying. I would not go to any orthodontist if I wasn't 100% sure that what they were doing was the best course.
Good luck.