I was reading this article today that said the youngest child is usually fun loving, craves to be the center of attention, and is a risk taker that gets bad grades and has a sense of entitlement.
While the Oldest child is the only child in the family that had his/her parents undivided love and then loses it. Thus older children continually try to achieve to win their parents love back. So they get good grades in school, avoid risk, become corporate leaders.
Middle children tend to be more social oriented and try to please others and don't do much else.
Only children turn out most often to be psychopaths.