There is not a way to share just your date of birth. After providing your PIN it can read more than just your date of birth.

That's... partially true.

If you use the _digital_ MyNa card (e.g. the one in the Wallet.app; not the plastic one); the iOS SDK lets you only request the "is user more than XX years old" flag; without getting the actual identity: https://developer.apple.com/documentation/passkit/requesting...

Now, AFAICT nobody actually does this, but the technical ability is there.