I really don't know how you should dress. First, it depends of the wedding, if it's big or not and how formal and traditionnal it is. I would say it also depends of what suits you and what you feel comfortable in, even what you usually wear. At your age, you are somewhat in an in-between. Some teens your age might feel comfortable wearing a lot of make-up, even in everyday life, and that look will suit them, for example, but at that age I wouldn't have felt good at all wearing make-up the same way women in their late teens or early twenties do. Very little or maybe even nothing would have been my choice, but then that's just me. The same goes for the dress. You still want to feel like you are yourself and not look as if you had unexpectedly aged a few years.

It's definitely tricky to dress for such a day at your age, especially since the groom is your brother.
I would suggest shopping around with an open mind, just trying to get a general idea of what you think would be a nice attire. Then, if you are not sure, try to bring somebody with you to tell you if they think what you had in mind is appropriate. You could also ask other teens or young women what they will wear at that wedding, that might give you ideas.
