Yes, I never said that women are statistically as strong or aggressive as men,
Generally speaking it's not strength or aggressiveness that prevented women from being used as soldiers, but their status. Unlike men who are sexually expendable, each woman capable of birth had a tremendous value in pre-industrial society. Woman was a prize men fought over, and one of the main spoils of war. So sending women to fight when the whole point of this fight is to protect them is not a very smart idea*.
In terms of an actual capability, the thing that makes women less capable in soldiering is not strength (that's of little consequence in actual warfare) nor aggressiveness (that determines career choice, but has little impact on performance) but endurance. Army is not for fighting, but for marching - and unfortunately, we are not built to withstand murderous forced marches the same way men can.
However, when speaking of RPG characters, we usually discuss not soldiers, but warriors. Warriors are outliers in every society, career bloodletters dedicated to their craft, not ordinary folk. If cultural factors don't play a role limiting their participation, a fantasy society resembling earth could easily produce female warriors - probably not as numerous as males, but a substantial number. And the less earth-like the setting is, the more this discussion becomes irrelevant. Sure, the average woman is less suited to be a fighter role than man - but warriors are not ordinary.
*That's also why we have very little historical accounts of female soldiers, but remarkably more of female warriors. It makes sense for a female to take a fighting role in a specific set of circumstances, but no sense to participate in organized warfare.