I do a lot of historical RP, it's my favorite genre and while I can play male or female, I tend to prefer female characters. I try to keep the role historically accurate as possible, bearing in mind what culture and time period the story is set in. Currently I have a Viking age RP going and my main female character is strong, fiery and tough but she's no raider, nor does she walk around in armor. She use a spear to defend her home and children but is not an active warrior. Her strength lies in her cunning and character, the support she gives her husband who is a warrior and not in her own sword arm. It does not make her boring to play, in fact it's more entertaining because she does have limitations and working around those allows for more creativity than just striking it with an axe. 

I don't see a problem with stretching it in a historical fantasy type RP, because it is fantasy. It would depend on the GM's rules and what the world lore allows. 

As for gender ratio, it all depends on the circumstances. I like a realistic ratio, if its a war situation, there will be more men than women unless you're on the homefront where it is likely to be the opposite.