My pre-teen....

Being the oldest of four HAS to be tough... You're basically the "parental science experiment" for any and all siblings who follow. Parents don't get the instruction manuals and decoder rings.  They "wing it", go by instinct, and do the best they can. Being a little more aware of what to expect on the next rounds, makes it easier... (Although once you think you have it figured out, nature throws you a COMPLETE curve ball and the next child is something COMPLETELY different in every way possible. I'm not talking about a little. I am talking "Are you sure you two are even related?" different, but that is a different post all together...)
Then to top it off, there are examples to be set, expectations of being "the leader", the responsibility of helping to care for the younger siblings, and having gone from only child to not... The subsequent children don't know what it's like to be a lone child. They come into the world having to share time and, well, everything, whereas, the eldest... Maybe not so much.
I try to keep this in mind when dealing with my pre-teen. He has not one, not two, but THREE younger siblings to contend with, and since they all have such strong and dominant personalities... Well, it gets interesting.
I'm the baby of the family, so I can't necessarily relate. Lucky helps out quite a bit in that arena being the eldest of three brothers and he is constantly trying to remind me of the position that my oldest is in when he is being "difficult". In looking at the situation, I guess I can honestly say that maybe perhaps there are times when I do expect a lot from him. Not because I am demanding that he do more than his share or make him do something well above what he's capable of, but in trying to look at it from his point of view, in comparison, it can seem like I ask him to do more than his brothers and sister.
Then there is the fact that there are four of them.... It's not always quiet, it's not always, civil, it's not always peaceful and in the grand scheme, it's not always fair. And what makes it "not fair" is having to hear, "because you're the oldest" or "because he/ she's younger than you".  It's the blanket response to "Why is it okay for HIM/ HER to   eat cookies on the floor/ play with my stuff without asking/ hit me, but I can't hit back... The list can go on. And in all honesty, he does put up with quite a bit. He does have a very high threshold and tolerance for putting up with his younger siblings (especially his sister whom he has a soft spot for) and as far as the role of big brother, he is awesome at it. Better than most.