Pretty sure the owner is just doing this to get some free advertising and to virtue signal. "See...I'm one of the good guys who doesn't sell to anyone under 21!"
In other news had the school district not had a liberal policy of looking the other way when Cruz should have been charged, he would have been flagged and unable to purchase a firearm no matter what age.
I keep hearing how the police responded to his house 23 times in the year leading up to what happened. Not to mention I seen posts he made on social media websites in news links how he (Cruz) stated "He was gonna be a professional school shooter".