Um, breathe? Servers get mistreated a lot unfairly. It was just an honest mistake, let it slide. I've worked in restaurants and have seen some foul mistreatment. Also, have you ever seen "Waiting"? I have never seen/done anything like that but I've heard stories of placing that would make you sick just hearing about it.
Also, grow a beard and the confidence in yourself not to be offended but such small things. Besides, think of it this way: you will be able to pick up younger dates when you get older. Also, you can win those guessing games at theme parks / carnivals a lot. My dad used to do that all the time. Sometimes, they would think he was lying when he claimed to be my father (I'm 23) because they honestly didn't think he was that old.