There are many apps available that perform age gating. That is the self-reporting popup that asks customer's for their birthdate. This is not a true age verification.
For actually accepting customer's ID documents such as a national ID card, drivers license or passport to verify age - there's our app Real ID: https://apps.shopify.com/real-id
We verify the authenticity of the document within seconds and you can automatically allow customers that are of age because our system can read the date of birth field on the document automatically.
First 10 ID checks are free, I'm also available to answer questions about ID verification and true age verification.