“Won’t somebody think of the kids?!” while they admit to using the data to squeeze more money from ads (translated making your experience better). They don’t deserve the communities they have anymore.
Soon any company you interact with will have enough information to ruin your life because there’s always a way for some employee to get the data even of you really do what you promise and don’t save anything.
As GLaDOS said - it’s been fun, don’t come back.
Zero-knowledge proofs and anonymous attestation - the problem is you still have to prove your identity and age to some trusted entity using a certificate, similar to a physical ID. But if you can get that, you can then anonymously prove your age. Assuming the verifying site trusts your issuer. Also assuming they trust you didn’t borrow somebody else’s device. Also assuming they don’t ask for more and more proofs until they can identify you anyway.