There's a fairly non-invasive way to do age verification: ID cards that connect to a smartphone app that only provide a boolean age verification to the requesting service. Requesting service can be anonymous to the ID app and the requesting service can only receive a bool.
That most implementation will try to collect far more data is the real concern.
Because if we don't have the keys to the machine, then we don't actually own our computers. If we don't own our computers, then we have no freedom.
Because everything the word "hacker" ever stood for will be destroyed if this nonsense gets normalized. The day governments get to decide what software "your" computer can run is the day it's all over.
In the modern world, this is like saying people under 18 shouldn't have the freedom to be able to read and write. We would be decades back into digital stone age if we had held onto such a preposterous idea in the 80's and 90's. Virtually everything we have now is basically built by people who were hacking on their computers in elementary school and exercising their freedom of speech in terms of writing code freely at the discretion of their own imagination.
Think about how the proposed idea would most likely be implemented. It would be used as justification for manufacturers to sell devices that the end use doesn't control. They already do that; this would give them legal justification.
That most implementation will try to collect far more data is the real concern.