The ICO and Ofcom have now published the anticipated "Joint statement from ICO and Ofcom on age assurance"
https://ico.org.uk/media2/5ybpmabf/ofcom-ico-joint-statement.pdf
This is quite important, since both regulators seem to want a piece of the online safety pie.
This would suggest that the only data that service providers have the right to retain is a simple boolean value to indicate that the user has attained the minimum required age.
I can't see this being the way that age verification is implemented.
@ReggieHere, AFAIK, that is how the EU proposed solution should work. But I have second-to-third-hand info on that, so please take it with a pinch of salt.
That said, even then, it needs something to prevent spamming the question "are you 18 yet" every day until you get a "yes" and therefore know the exact birthday. (again, I don't know if the EU proposal already covers that issue)
Neil Brown
Reg
Matija Šuklje