First of all, let me warn you I'm a dad. I have 2 sons, ages 14 and 11. And they annoy and irritate each other endlessly. However, they're close enough in age to be able to do some of the same things and get along most of the time we're in Disney.
On the other hand, I had a sister 7 years younger than me, and it was really hard. She knew just how to annoy me, and I was always the one who got in trouble. I don't know that I have a solution for you, but there is some hope. Years later, my sister and I became really close as adults. Not sure really what changes as you get older, but we have this really cool relationship now.
Just do the best you can for now. Someday you guys will really appreciate each other in ways that probably seem impossible to you now!