However if you're just mad because you think they are unfair, and you don't like it, get over yourself.
They likely train together because they are all at the same level. They want to go hard with each other, and get the most out of their training.
From the outside it may look like an elite club. They don't like kyu ranks and women. That makes you sad.
From the inside, it probably seems to them, like they want to train really hard and have found a group they are comfortable with. They feel safe with each other, and can explore Aikido together.
It likely doesn't have anything to do with you, kyu's or women.
I have to disagree that exclusion is appropriate in an aikido dojo. Working with kohai helps teach us the patience, humility, social responsibility, and generosity that are intrinsic to our art. I would even say that it's the responsibility of sempai to actively try to work with kohai. If those guys want to train together, they should do so at an open mat time...