Interesting read.
I have a sister that is 2.5 years younger than me. We were never close growing up. We didn't get along very good. We didn't fight, but we basically ignored and were apathetic to each other for most of our teenage years. I have a brother that is 8 years younger than me. Though he and I weren't close enough in age to really "hang out" very much, we have grown to be pretty close once he got to be a teenager. Now he is almost 20, and we are as close as ever. I would like to think that some of his personality was influenced by me. Not that I deserve much credit, but that some of the positives I see are because of our interaction. He is an incredibly good kid. I'm very proud of him.