So, I can see where commercial OSes, like Windows and MacOS, but maybe including Chrome, Red Hat, and similar, would welcome the requirement to collect user ages. Another piece of user data for telemetry, ad serving, etc, with the cover of 'government made me do it.'
Linux is always going to have weirdos, ready to spin up their own distribution for their own reasons. Like, I remember when the majors all started switching from init to systemd. There's still a bunch of distros, even some good--sized ones, that avoid systemd. If age verification works its way from facilitating tools to distro mandates, I guarantee that there will be distributions created in jurisdictions without age mandates that exclude any tools that require age validation or with systems to spoof age validation. It's simply too easy to change linux to avoid this.