I'm suspicious of a young looking customer
Why do you think they are suspicious?
He shopped at the checkpoint area! Why would someone shop there?!
You are wary of a young customer because of where he was shopping, but then why are there things to shop for by the checkpoint anyways? Take the shopping venue away from that area and you won't have to see anyone as suspicious anymore.
I'm human, it's okay to not be suspicious of someone.
Maybe you are confusing suspicion for paranoia. If people are shopping and buying things you shouldn't assume someone is stealing because of their age.