Ok, I guess some slip through because they should normally require age verification. Even medical videos like breast cancer screening are classified.

Does Google have a reliable way of doing age verification on YouTube these days, or is it still as easy as creating a new GMail account?

In EU you need to upload your passport.

Or steal your parent's credit card. Its an American company after all they use their CC for everything and a CC is completely normal for identification for some ungodly reason that I do not comprehend.

Just to resgister an account? Is this a new change? It's the first I hear of it, and I have family members with GMail accounts who were <18 only few years ago.

Not to register an account, but any video flagged as any kind of explicit, suggestive or problematic content requires age verification. There was some flack recently as YouTube was requiring age verification for LGBT+ support videos.