Other countries also have Call of Duty, but not such a big problem with mass shootings. So I don’t think its that easy. I think it is more interesting, what the NRA is doing. Such a big and powerful lobby organization should have way more influence, than a video game series.
Sounds as dumb of an idea as the one child policy
Which then wouldn’t be a legally full verification of your age, thus the legislation would probably require some other means. We currently have a similar discussion in the EU regarding porn sites. Verification methods could be showing your id card and your face to a webcam, or showing up at a verification office in person (at least in germany we have this with our national postal service). Of course the porn sites don’t want to implement this. And I cannot really blame them. Nobody would give a random porn site their real identity and it would still be very easy to get porn without verification.
Age verification on social media is very similar.
An interesting customer base might be small communal organisations. At our local scouts troop I had a discussion with a friend, who is also in IT. His idea (not fleshed out) was to provide small local organizations with a stack of already configured open source software to support the typical needs of such organizations (like a wordpress website, a nextcloud for file storage and common calender, limesurvey for surveys and event registration, mailman3 for mailing lists,…). Depending on the needs you could sell the initial setup process (your personal work in setting up and skill transfer) or ongoing support. Though such organizations normally don’t have much money to give away. So probably its not really worth your time financially (though probably really appreciated in the community).