Say a little 10 year old wishes to be baptized. The parents beam with pride with how mature they are and can hardly wait to see them baptized.
The same 10 year old child tells his parents that he has thought about the religion and has decided that it is not right for him. Therefore he wishes to opt out The parents are frantic. "You are far too young to make such a serious decision" They tell him that as long as he lives at home he will be forced to continue with all aspects of the religion and if he opts out as an adult even if not baptized he may well have to leave the family home. The Elders applaud in support.
My simple answer to this kind of issue is that if a child is not old enough to say NO and quit they are not old enough to say YES to being baptized