I think that's why me and my sisters get on so well. I have a younger sister who's 20, I'm 28 and my older sister is 30. My sisters don't have to "compete", because of the big age gap and I don't have to compete with either of them because I'm a bloke.
Probably the most strained relationship (relatively), is between me and my older sister, probably because we're so close together in age. We grew up together, we beat each other up, we blamed things on each other, we broke each other's stuff... She still jokingly reminds me of a time when I was about 1 year old and I threw a door-wedge at her face and drew blood (no idea how she can remember something that happened when she was 3).