Looking young should make you feel great about yourself. I look really young too so people often talk down to me. However once I open my mouth they realise I'm older than I look. I enjoy the look on their faces when they realise that. So I think it's what you saying as well, how you come across. I'm not super confident but am good at faking confidence. Perhaps try that? Speak with a bit of authority in your voice and you'll get the respect you deserve. You'll always come across rude people, but please don't allow them to make you feel bad. Don't give them that power