I personally believe this should be controlled at a device level, not at a state or national level. But on a theoretical basis, yes, you could use so-called "s

I personally believe this should be controlled at a device level, not at a state or national level. But on a theoretical basis, yes, you could use so-called "soul bound tokens" attached to an Ethereum address, for example, for this use case. A soul bound token is similar to an NFT, but cannot be traded. It is bound to a particular address. So in theory, you could go through some service provider for the identity verification, give them an Ethereum address to attach the 18+ SBT to, and then you could simply sign a message from that address for any website that required 18+ verification (would cost no gas, it's just a signature). See Vitalik's blog post on SBTs for more info: https://vitalik.ca/general/2022/01/26/soulbound.html https://vitalik.ca/general/2022/01/26/soulbound.html