I have recently started a new job, and everyone is female, so about 25 women of varying ages. That said, most are under 30.
I was working in a predominately male environment before (about 70:30) and found it very easy. We had a laugh, there were no cliques and it felt very relaxed.
I'm going to sound very sexist, so let me say I know some women don't do this and working with men isn't always easy either, It depends on the individual. But when women are in a group it can often feel like school all over again. Gossiping, cliques, snide looks, secret laughing etc.
In this new job I feel isolated, all the women have their little groups and don't like newcomers getting involve. They all have secret online chats, and I've seen then exchange knowing looks with each other and laughing. They spend their lunchtimes gossiping and it feels like a sixth form common room. I've tried to get involved but it's not very inclusive 
I don't hate women - I am one! But I'm finding this working environment quite hard to deal with