For me, growing up, the paradox my parents presented was that every quotidian detail of their lives was regarded as top secret. "Nobody has to know!" my dad always insisted. When I was in K they told me, for example, that my dad was 25 & my mom 23 (add two decades to get their correct ages). Yet nothing about me was treated with confidentiality. I recall hearing my mom on the phone talking about this or that, however cringeworthy, to our neighbors or her friends. I think that's the way parents of the WWII generation were raised.

It's not a bad thing to teach kids discretion, but as you point out there is an age where filters are non-existent & it's wrong to expect otherwise.