Personal combat skills should differ depending on sex

So a dweeb like Littlefinger who can barely hold a sword would receive a combat stat boost for having a penis while a hardened warrior like Brienne or Ygritte would be punished for not?

There's already limitations on when a female character is eligible to lead armies, be knighted, fight in battles, etc which handles it in a more dynamic way that a arbitrary mass applied stat increase. Your Sansa type female characters are not on the battlefield just like your Littlefinger type male characters usually are not or get killed if they do.

I'd suggest a trait or modifier that is something "egalitarian notions" that enables you to train girls, rather than making it dependant on strength etc,  dornish and other largely gender neutral cultures should have a higher chance of it and it should be low for the rest of westeros, it's basically like how Ned arranged for Syrio to tutor Arya,

Generally even the structure person to person applies, and this would be better represented by using a broader array of genetic traits anyways, since some women *Cough* brienne *Cough* are built a lot more sturdy than most men could ever hope to be, while some men are pretty useless as far as physical development goes. Generally their are other reasons why women tended not to be soldiers in many cultures besides just physical differences, since many women could successfully bulk up if need be and depending on lifestyle often did just doing heavy labor like trying to make a cow go where it doesn't want too. The way game of thrones is presented one could argue that there are a fair few more chances for men to be physically deficient simply because there seem to be a lot of fat poorly maintained men than women who let themselves go, so there's a good chance if actually trained the women due to a healthier lifestyle would actually be more capable.

Now if only some of their brothers would realize unhealthy guys tend to be easy targets for succession by knife.

Yeah I'd also add that even though there are physical differences between men and women that doesn't mean there aren't ways around it, sure you have fighter like brienne who fight like a traditional Westerosi knight would, but then you have characters like Arya who focus their training on speed and agility saying that men are better fighters because they are usually bigger and stronger is to adopt a "Gregor smash" mentality which just isn't correct

Yes he should and this +10 bonus will mean nothing compared to superior training and other traits of those two. I meant an AVERAGE man vs an AVERAGE woman without other traits or training. This game has other arbitrary mass stats for children and teenagers so why not to differentiate men and women. It is true that an exceptional woman like Brienne can beat many men but this is an exception. If Littlefinger had twin sister with the same traits and fighting skills he would surely had an advantage over her for having testosterone enhanced male body type. Pure biology.

But it is already. If we apply a +10 bonus to all men, women with strong trait still will have an advantage. But even the strongest woman will never have the strength of the strongest man. Just look at weightlifting records and other examples from real life.

en.wikipedia.org/wiki/List_of_world_records_in_Olympic_weightlifting