The only sibling I have is my autistic twin brother and we get along fine, he's like a really close friend to me, although we can't exactly have proper conversations. I really never understood why siblings couldn't get along. XD
Then again, I have a younger cousin who's six years old and I guess you could say she's like a sister to me. She's constantly at my house playing videogames with me and I take her to see movies and whatnot. Again, I rarely get annoyed at her unless she's just being outright annoying on purpose.
I don't know, I guess I just developed more tolerance towards younger children from growing up with my brother. XD