I'm both the oldest and the middle. Let me explain...

My mother had her first child with another dude from a previous a marriage. I'm my dad's first child. I have characteristics of both oldest and middle child and though my brother is technically the real oldest I'm the most responsible and the most awesome talented talented. (I will also probably be the shortest)

Oh wait I guess technically due to the huge age gap of my brother and sister (they are 15 years apart) that does in fact make me the oldest. As he was never really in the household when she was born nor was my mother.