1. Somebody looks up to you.
So you're motivated to stop YOLO-ing and to actually start living a decent life.
2. You get to live vicariously through her youthful milestones.
As you become a late-twentysomething old hag, you can continue to celebrate high school and college graduations, take her prom pictures and do her hair for her first date. #aww
3. Hot younger guys are always around.
Go ahead. Facebook-stalk her cute friend Miguel. It's not creepy at all.
4. You can rely on her to tell you the latest fashion/slang/social network trend among the Youngs.
How I learned about crop tops, Snapchat, and One Direction. Thanks, sis.
5. You probably have hilarious stories of kicking her down the stairs when you were little.
I picked my little sister up out of her crib when I was 8 and dropped her headfirst on the ground. No lasting damage! All the LOLs!
6. You feel super big-sisterly and responsible when she turns 18.
And when she calls you from the bathroom of a bar, asking you to get her, with vomit in her hair. Being on the other end of that "leaving a glass of water and some Advil on the night table" situation feels pretty great.
7. You can dole out advice based on mistakes you've made.
Not that she'll always listen to you. Everyone needs to have that one awful heartbreak in order to become a real adult.
8. When she achieves something amazing you're so proud that it almost feels like you did it, too.
Genes! My little sister is taking up an honor's course in this university AND is dating the campus hearthrob and I brag about it almost as if I were not the idiot of the family.
9. She always got the stuff you pretended to be too old for but secretly wanted anyway.
Like One Direction.
10. She always covered for you if you got in trouble.
Because you'd totally do the same.
11. You automatically had a nemesis until you were 18, and a best friend thereafter.
She stole your makeup and lied about it for six years, but now you guys can bitch about your weird family together so it's all good.
This article originally appeared on Cosmopolitan.com. Minor edits have been made by the Cosmo.ph editors.