As an older sibling, you can help shape your siblings to a certain extent. As a teenager with a much younger sibling, I have tried my best to help protect my little brother from some of the ugly aspects of the world. I want him to grow up confidently and pursue whatever dreams he may have. I want to expose him to a world in which he mustn't conform to the ideals society has set out for him, including gender roles.
Gender roles are pushed on children from birth, when they are given a blue or pink hat depending on their gender. Fast food restaurants ask what gender a child is, so they can give the corresponding boy or girl toy in a kids' meal.
My younger brother is four and is still figuring out who he is. Some days, he'll want to go play soccer, while others, he would be happy drawing a picture. I always, out of interest, ask him what his favorite color is. It changes daily, and sometimes it's pink. If you ask an older man his favorite color, you will rarely find one that will admit to liking pink, because society has coined it a "girl color," however my little brother has yet to be corrupted by society in this manner. And that makes me happy.
I've seen parents that ask their child which lunch box they want, and if their son says they want the pink one, they try to suggest something more boyish. What about the blue one with sharks? I think this is wrong, and we should allow children to figure out what they like on their own, rather than slyly trying to push gender roles on them.
Let kids be kids, and don't try to force gender roles on them when you don't need to.