Let's say someone is 22, how can they credibly attest to being older than 18/21 without referring to some sort of government record?
They could produce their parents, or any witness of their birth.
They could (if they were born wealthy) produce a hallmarked silver spoon engraved with their name. Not proof, but persuasive.
They could produce their 21-year-old younger sister, who has government ID (yeah, I know, that is a resort to government ID).
Best of all: they could produce a birth certificate, signed by a doctor (not itself government ID, just a prerequisite to getting a government ID).
1. How would you verify that's actually their relative and not a friend or stranger? 2. How do you verify that they are in fact the older sibling and not just saying they are?