It's not simple, but it's also not new. mTLS has allowed for mutual authentication on the web for years. If a central authority was signing keys for adults, none of the protocol that we currently use would need to change (although servers would need to be configured to check signatures)

and is it easier to implement id checks for each online account that people have, had, and will ever have in the future?

parents need to start parenting by taking responsibility on what their kids are doing, and government should start governing with regulations on ad tech, addictive social media platforms, instead of using easily hackable platforms for de anonymization, which in turn enable mass identity theft.