Discord says they'll use some AI garbage tool. Those are prone to mistakes over a large enough userbase. It will not be a rare occurrence for an adult to be labelled a child until they debase themselves with a scan of their face or a copy of their government ID.
For children - this mandate also still makes the decision on behalf of the parents that a child must submit a scan of their face to a third party. Moving to Persona for age verification involves verification data being sent outside of the user's phone - in direct contradiction to Discord's initial promise of keeping facial scan data solely on the phone. Third parties that we've been given no reason to trust will delete the data without using it for an improper purpose such as creating derivative info from the ID or facial scan itself unrelated to the sole purpose of verifying that an individual is an adult.
While we're at it - is there any legitimate reason why Discord is associating a person's actual or estimated age with their account as opposed to storing a value that states if they are or are not an adult? That sort of granularity seems unrelated to the stated purpose.
I don't love what discord is doing, but where are you getting the idea that discord is going to estimate the user's age using "some AI garbage tool"? The article says everyone is on "child" mode by default, and verification is only required if you need to use the features / access content marked as adult only.