PF

I have searched and searched and can not confirm this answer. Her is the situation. I have a 16 year old son. He pretty much goes every where I go. On multiple situations I have been denied sale of tobacco or beer because he is with me. For example on Saturday I stop in a convenience store to get my once a week pack of smokes (can't fully quit). SO the guy cards me I think "cool I am getting carded at 37". Then he asks for my sons ID. I say there is no need for that. He says "it's the law". I say I know it is a store policy if multiple people come in to card them all . However he is my son. We were not both carded when he was 6. I am pretty sure this is not a law. However if I am wrong can someone please let me know what statute it is ?