No one should have the ability to exploit underage, developing, unaware children and teens regardless of, well, any factor really. *shrug*
Can't drink alcohol because of long term health risks, can't cause and receive repeated concussions because of, well, long term health risks.
Also, this isn't a matter that can be side stepped by private leagues as it involves the physical well being of minors. They full stop do not have the agency to sign off on sacrificing their body and health and adults don't have the right to make or encourage them to harm themselves either be them parent, teacher or club manager. It will become more apparent how irrelevant volition is as the research into just what we have been doing to children continues to pile up.
Child labor brought in far more money for more people than underage football ever has and we were able to abolish that for much of the same reasons, so it's only a matter of time before the issue of whether we should be able harm our children for the sake of a game is settled regardless of opinions.