With vErify you can now also verify the age on checkout. The customer needs to enter some digits from a personal ID card (Germany) or an international passport to validate the entered birthdate. You can set the demand of age verification for all your products or only for specific items. You can also set the shipping countries for those products as well as the minimum age.
Feel free to try it by ordering this product right here and proceed to checkout.
Don't worry - you won't get charged for this ;)