I've been having the urge to cut my sister off, even though she is so young.
Why would you think of doing that?
Our relationship has been toxic throughout my whole life
It's bad to cut someone off who is so young, because they might not even realize that they are hurting you, and will still have plenty of time to improve.  However, if your relationship is truly toxic, then you may want to spend a lot less time with your sister, just remain open to contact.
My sister is so annoying. I hate her.
I get that she can annoy you sometimes, but you need to understand that she is young. When she grows up and matures it most likely won't be an issue for you anymore.