I'd have thought an OAuth flow to a government run ID system, to create an account you first must verify your age by redirecting to the ID provider logging in via FaceID/Fingerprint to verify it's you and then you are redirected back to the original site with a verification code.
Admittedly on paper that means the Gov system would know which sites you were approved for, not logging that would require legislation to not store these logs.
A local beer in a bar will normally be around 60k IDR so $3-4, wine is more expensive generally in SEA you'll normally pay around 90-100k IDR per glass.
If anyone is interested Gruf Rhys (from Super Furry Animals) made a film, Separado!, where he tried to track down his Welsh family that migrated to Patagonia.