Thanks for your insight on this.
Now to find a shop that carries a selection of this type of boot...
I think you are asking about flex and yes everybody makes one, but I don't think anyone his age can be competitive in a 90 flex boot. 90 flex boots are jr. boot. The cuff is low and the plastic not stiff and often with a low quality liner. The design does not promote powerful edging and at this point although he is not heavy he is probably starting to ski with technique that is building speed through the turn that requires solid edging and this simply is not available from a 90 flex boot. Why not move him stiffer and if it is too stiff let the coaches decide. the boot can be softened forward and still have stiffness laterally that he can probably use now.