I think birth order is just part of all the rest of our personal experience. I remember telling my T once that I grew up "alongside" my brothers and she liked that. No matter what, one's relationship with the parents and the rest of the family and outside world can't be the same as any other sibling's, even if one is a twin.

I was the youngest of 4 and the only girl, the "precious, darling, baby girl" but my mother died and my stepmother and her daughter, older than my oldest brother, became part of our family and a great deal changed. I don't think anything can be "predicted" or said for sure about birth order that makes any difference (yes, the oldest is going to be asked to look after/care for the younger children and to do other chores) and there's no predicting how one individual child will respond. My husband and my brother are each oldest children of four but are way different, even though my husband's and my families had similar backgrounds (our fathers were both Navy officers) and upbringings and the children are similar ages. I think more rests on "who" the child is to begin with than "where".