I think age restrictions are a misguided attempt at fixing the root issue. I am not against draconian legislation against social media giants, but age restrictions on the internet will negatively affect everyone other than the social media giants the most. I think the main problem with social media right now is the incentives that the tech companies have to optimize for engagement above anything else, and the reason they have that incentive is simple: targeted ads are an insanely lucrative business model. The fix is pretty simple, but draconian: ban any form of targeted advertising on any digital platform.

Age restrictions will just cause a loss of privacy, increase the risk of government censorship, increase the risk of government misusing this for imposing morals and risk causing smaller independent sites to become inaccessible to the young even if they don't actively promote inappropriate content (I will also claim that defining what is child-appropriate content on the internet is impossible). Last but not least, the proposed technical solutions for this, at least in the EU, rely heavily on technologies such as Google Play Integrity and Apple App Attest, which means that they basically require EU citizens to accept Google's or Apple's TOS if they want to participate on the internet, and further preclude them from using an alternative open source operating system such as LineageOS or GrapheneOS. This alone is enough of a reason that I am fiercely against this, but it is by far not the only reason.

Keep the internet free and open for the users, but regulate the hell out of predatory business models.