In general, I argue for less state control on anything. But your argument seems flawed from its core. If someone is a bad parent, should we simply ignore it and let the children turn out idiots as well? And the line is often blurry, so that's why we designed schools that should compensate even for dumb parents.

And, just to be clear on this topic, I think these age restriction laws are mostly bullshit, but I'm deeply against the concept of putting all the responsabiliy of raising children onto the parents.