I used to physically fight with my sister a lot but I don't anymore. It's not because I like her more now, just because I used to really hurt her... it's scary thinking about it now, and also because she always tries to fight with me and so I feel that I need to be 'the sensible one' otherwise it won't end well.
I also used to argue with her all the time but I don't do that so much anymore either. The reason for that is because if I try to argue with her, she'll just walk away and start crying... she's not as mentally strong as I am, so I try to avoid confronting her etc.
If she was as mentally strong as me and didn't have a problem with confrontation, I'm sure we'd argue all the time. She does annoy me a lot and sometimes it's difficult to keep my mouth shut.
I don't think you should worry about the future. Most of the time, I really do hate my sister, but I'm sure that we will be friends when we both grow up. The main reason why I get so annoyed at my sister is because I have to spend so much time with her, and when I get older, I won't live with her and I'll hardly have to spend any time with her at all, so her annoying habits won't show through so much... and she'll be more mature.