I get that alot too! One time the Jahovah Witness came to my house, and FI answered and they said, "Is your daughter home?" lol You should have seen his face!!! Also, one time I was at a Parent Teacher Conference (as the teacher) and my student's parent just started laughing... and he said, "Ummm please dont take this the wrong way, but how old are you? I am worried that my sons teacher is in highschool" ( I was actually pissed off)
I think extra mascara/eyelashes and makeup will do the trick for your wedding. Maybe if some of your hair is up. Believe me no one will mistake you for his child bride! You are going to be beautiful!