There are solutions to this. Look at how state ID on iOS is handled.

There’s an enrolment process where your identity is bound to your phone, and secured using biometrics.

When you need to prove age, the device can produce a signed token attesting to fact that your older than 21 etc. and your device is trusted to validate your identity using a biometric scan performed by your phone.

All of this is dependent on everyone trusting your phone to both validate your physical identity before signing something, and also not sharing anything it shouldn’t. But given you can already enroll US state ID on iOS, those problems are clearly solvable.