Both of my sisters are much older than I am. One was already married and had her own daughter by the time I was born. There is a twenty year age difference between us (almost to the day.) She is also the one that I’m most like. My other sister was 15 when I was born. She considered herself my mother. I went everywhere with her when I was a child. Even on her dates. All I had to do was stand in the front door with trembling lips and her date would finally relent and say “Go get her.” Now that’s a sister.

(I couldn’t find an author for the above quote. I always try to attribute quotes to their authors, if you know, please update me.)
Re: You are most like your eldest sister: I have 4 boys and a girl (who’s no 2 in birth order). My eldest son who is 25 and no 4 child who is 10 are so alike – personality wise ; as is no 3 child (18) & my youngest son (8)! I am the eldest in my family and have only one sister – we are chalk & cheese in looks, views, hair colouring, body shape, hobbies, personality …. complete opposites and yet we share the same parents!
You are correct, my eldest sister and I are so similar and sometimes we look at our other sister like she’s from another planet. But my eldest sister was already out of the house when I was born. And since my other sister was 15 when I was born, I am very close to her because of everything we did together. (All those dates I went on with her.)