Didn't remember of this, but it could work as well indeed. There is nothing stopping you from having a conversation with your parents or another family member to have him register for you in an exchange (be it CEX or P2P) and then he/she buys whatever amount you ask him to. He then can send you the amount whenever you reach the legal age to start using the platform or to continue accumulating in any other medium that you want to.

This method is used, from what I know, by parents that want to buy their kids investment options (such as Index Funds) instead of opening a savings account for them. So it could work for Bitcoin as well.