Kinda weird, but like everyone's saying, it's your property. I'd go with all but stallions allowed and just find the right boarder with the right horse rather than just mares. You could just as easily end up having a bunch of mares fighting all day as you could have with geldings. My gelding can't be out with mares, but all the others I've had could, as well as most of the ones I worked with at my last barn. It's more about the individual than their gender.
I give myself very good advice, But I very seldom follow it