Children are under parent/guardian supervision and they cannot make risk assesment and accept risk it makes sense to age restrict risky items.
What I said obviously speaks against your own body as well. The fact is if you have a secular government and a democratic one at that they lack authority to do many of the things they are doing. They exist to govern liberty not enforce world views and keep people from hurting themselves. Democracy should be like Unix, if you decide to shoot yourself in the foot it should enable you to do it in the most efficient way possible.