I look exactly like I did in high school and I'm 27 now. People always assume I'm in my late teens and they always do a double take when I tell them how old I actually am. Cashiers treat me with less respect than someone younger who wears make-up (I don't) and wears nice clothes (I don't do this either, all my clothes are black and somewhat alternative-looking and most of them are very cheap). I've been rocking alternative hairstyles and clothing for several years now and I'm used to being treated less favorably (although this was happening when I dressed normally as well). When it does bother me, I remind myself that if someone judges me solely because of my appearance, that has nothing to do with me and everything to do with their own maturity. I might look much younger than I am, but at least I know to treat people with respect

My advice is not to let it bother you. There's absolutely nothing you should feel bad about