You could also limit human female characters to a strength of 16 out of 18 or something like that. I already do that myself for role play purposes. Anything else just doesn't seem realistic to me.
Actually, I personally feel that the "female characters have less strength" idea is not correct. True, on average, males are stronger than females. But it doesn't mean a female hero should be average .
But that's just my opinion (and knowing some physically strong women and emotionally wise/intuitive men ).
Physically, men and women in our reality are different. Starting by having different sex!!!
Then, supposing some "stereotypes" as bonus/penalties based on sex for the humans in PE (or any other race that has a biological history of segregrating tasks), we could have (as example):
Males +1 Strength/+1 Constitution and Females +1 Dexterity/+1 Will. The system has some minimum and some maximums, like minimum for each stat is 3 and maximum is 18, having a 10 in each stat being the baseline for the common human (or whatever race).
The fact that some women can be stronger than men and some men can be wiser than women is because not everybody is born as a baseline common human. Yeah, the may get the racial bonuses but their stats may not need to be all 10s (being a PC, he could use roll 3d6 for each stat, or use some kind of point buy system...). The "average human" does not really exist (or is extremelly rare) anyways. So those racial bonuses are nothing but a "tendency". If you score a 14 in Strength with a male (after bonus) and I score a 18 in Strength with a female (that has no bonus), the tendency in our cases is not true. But in the general picture of PE, your male may be true to that tendency and be stronger than most of the females of your male's race.
One of the groups with issues about having bonuses based on sex are munchkins/powergamers that deny their nature and say that if females have less strength than males, they would feel forced to not play female fighters because they would be at disadvantage. But hey, the one writing played NwN2 as main a female Fighter/NeverwinterNine dual wielding longswords (that require quite the dexterity score) that had like 14 Intelligence and 12 Charisma (and invested in skills like Spot or Tumble). Yeah, I think my character had like Strength 14 at level 1. Any munchkin would kill me for such bad build.
I don't care one way or the other about bonuses based on sex though. I think that they are nice in the same way as racial ones but I won't lose sleep about them.
More on topic, I have read many times that people don't want their sex choice to impact the game (lets keep romances out of the equation...) beyond the proper recognition of the PC's sex in the conversations. Hopefully, that doesn't include having social issues in a fantasy world with societies that are not real. So much for "roleplaying" if not.