The age-gating is done in the background magic of the AI, determining general topics the user talks about, or things like the times of day the user is on ChatGPT.
It will not require mass-identification of the user base, unless you want to complain about getting age-gated to the «teen experience.»
To do this, you can upload a selfie to ChatGPT in the Account Settings, by clicking on Age Verification and selecting Verify Age.
From here, ChatGPT can determine your age from a simple selfie, but if that is not enough, you might have to offer up a Government ID.
On OpenAI’s Age prediction page, it says «this feature is still rolling out, so you might not see it yet depending on where you live.»
More at: OpenAI’s Age prediction page