I’m a woman, and, like several here, I’ve worked in fields that have been both predominantly male and predominantly female. I have to agree with the earlier comment that there are pros and cons to both situations.
In a male working environment, you have a very strict hierarchy. If you’re a woman and you start out in administrative work, it doesn’t matter how smart they think you are, or how much work you do, you have to be pretty extraordinary to work your way up on the totem pole. On the other hand, if you’re hired in at a higher-level position, as long as you remain straight-forward and somewhat aggressive, you’ll be OK. I’ve also noticed that, especially with older men, particularly if you’re working in a brokerage or other professional (not technical) field, they’re idiots when it comes to computers, and will absolutely refuse to take responsibility for any mistake. However, men are generally straight-forward, and far more matter-of-fact. You make a mistake, as long as you fix it and it’s not an enormous, asinine mistake, you’ll be fine.
With women, work relationships tend to be more complicated. The structure of the office, as noted earlier, tends to be more relaxed - your input is usually welcome, especially if you can provide a good, innovative idea that will solve a problem. However, getting involved in gossip will probably get you burnt, and you’ll probably have to deal with more emotions. For example, there was this woman where I used to work whose daughter had gone to college. She was a freshman. There was an administrative assistant working in our department who was just a little older than her daughter (a recent college grad) who became this other woman’s surrogate daughter. Said woman was also best friends with the marketing manager (also a woman). They all used to go out drinking together, and, even thought this assistant was awful, no matter what she did, she was golden. Because I didn’t have a closer relationship with all the women, I was left out in the cold and also left out of the information loop. I felt I couldn’t do my job well because of their relationship and eventually, for a myriad of reasons, left.
Regardless, good luck. Be prepared for mothering, and try to find a good balance of sharing a little of yourself, but try not to invest too much emotion into your job.