"government" age verification app will be made and maintan ed by some corp anyways.
so it will gather extra data, sell it sideways and leak like hell. (as they already do with all the data they already have)
I'm imagining something like recreation.gov in the US - it's the portal for booking campsites and other activities at national parks. It's run by BAH at great profit - most of the fees we pay aren't going to the national park service, it almost all goes to our corporate overlords.
Since it requires Android or iOS, Google/Apple can gather the same data too.