Basically, I'm revisiting this question: Under age users - could they just be suspended until of age? Instead of immediately deleting an underage user's data, consider the following protocol:
Underage user protocol:
- Stack Exchange creates an encrypted ZIP file of that user's data,
- Stack Exchange securely stores the encryption key,
- Stack Exchange sends the encrypted ZIP file to the underage user [who cannot decrypt it],
- Stack Exchange deletes the user and the encrypted ZIP file [keeping the encryption key, containing no PII].
In this way, the underage user stores their own PII---if they delete it, it's permanently gone. And it's not decipherable in the unlikely event that it's sent to the wrong user. Stack Exchange does not store the PII of an underage user.
Protocol when they reach age x (where x is their locally required age):
underageuser sends the encrypted ZIP file to Stack Exchange [if they choose to do so].
- Stack Exchange decrypts and restores the user's data onto Stack Exchange.
Would this work?