Among the biggest legal problems with age verification being that most developers aren't in the USA nevermind the specific states these laws are being made & passed within, and thusly it's a matter of a state within a nation trying to make & enforce laws on an international basis.

*The biggest ethical one being it's logical fallacy of claiming that it is the job of the government and technology companies to supervise children directly, instead of parents & individually designated guardians. Linux & open source overall is mostly about exercising greater autonomy & individuality than exists with big tech entities, so it complying with it is to turn against the mainstay of it's central ethos.