On that police video wasnt asked to verify age, but I expect it will come, they likely doing a progressive rollout.
The problem I have with sending ID to verify age is I think it adds risk for ID fraud, the internet needs a different way to verify age.
On the NHS app I was asked to read out numbers whilst showing my face, that would be a way to visually verify age as an example without sending off official documents and just hoping they dont get compromised. People who struggle to look over 18 would still be a problem, but it would be good enough for those of us who are much older than 18.
I also have multiple youtube accounts, so I would hope the age verification links them and works for them both.