Doesn't matter, I've already had to provably identify myself, the information is a) out there b) will be used and stored, and c) will be abused

and there is nothing I or the few (in terms of power) well-meaning government and corporate actors can do to change that.

And how do they prove to me they (and no 3rd party providers) aren't actually storing the data? I simply don't trust companies telling me they won't store something, so to me the only acceptable option is the data to never leave my device.

Nope, as the article notes, it is actually almost never enough because it does not stand up to legal scrutiny. And for good reason: there's no way to conclusively prove that the platform actually verified the user's age, as opposed to simply saying they did, before letting them in.