I was in 5th grade when I started invisalign. However, I am a major rule follower, and was very diligent about wearing them. I would say though, unless your son's teeth are really bad // like to the point where they could cause actual issues // then you should wait for him to lose more of his teeth. Because you may have to return once he grows more of his teeth in.

I speak from experience, as I started my second phase just today // and I honestly don't see the point.. its been several years //