Every age verification system I have seen assumes you own a smartphone, that it is recen …

Every age verification system I have seen assumes you own a smartphone, that it is recent enough to run the app, and that it is yours alone.
Three assumptions. Each one excludes someone.
The teenager sharing a family tablet. The 80-year-old with a phone that makes calls. The person whose device is six years old and no longer gets updates.
The regulation says access must be non-discriminatory. The architecture says: install the app.
So here's the question I keep not getting an answer to: how do you prove you're old enough when you don't own the thing everyone assumed you'd own?