Is it bad if people think I'm younger than I am?

I'm 21. I recently went to a buffet with my family. The cashier asked me my age, thinking I would get a discount. I told her I'm 21, and she was like, "What? You're 21? I thought you were like 13!" I went to a casino where the guy asked "can I help you?" He assumed I was underage, since you have to be 21 or older to enter the gambling floor.

Is it bad if people think I'm younger than I am?
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