It seems that there's some kind of common belief among our society that the oldest child should be the one who's most understanding, to start with. In addition to that, oldest child is often expected to not trouble their parents. In other words, the oldest child should think of working out his/her problem on his/her own. Even worse, the oldest child is often expected to take care of his/her younger siblings, if any, because the parents will not live long enough to take care of the younger ones, they often say.
Simply put, it seems that our society believes that the oldest child is expected to give and not take. Unfortunately, this often causes depression for the oldest child, which is why some of the oldest children in the families out there happen to be trapped in the wrong way and can't seemingly go back on track, well, except for the very wise ones, I think.