This one is a hard one to answer for me, because I've been the youngest, the middle and the oldest. I'm the youngest of my full blood siblings, and they all left by the time I was about 9/10. My mother died and my father remarried and had two more children. For a while we were all at home, that made me pretty much the middle child (my oldest sister left home at 15). Once all my older siblings left, I was the oldest to my two half siblings.
Out of those two, I left first, my younger brother left several years after I did, my youngest sister is still in.