[Palmik]

As far as I know, there isn't a serious implementation of this that is ready for production and that has enough adoption in the affected regions (e.g. UK).

Chrome and Safari are working on browser APIs that seem reasonable, but will only be available around the end of this year. The various region specific identity providers (like GOV.UK One Login) will also need to integrate with those (possibly through Google/Apple Wallet or their own app).

That means one has to use shady 3p age verification services (like Persona) which do who-knows-what with customer data and cost on the order of $1 per verification.