What goes on is that media ultimately shapes and programs people into certain molds. They learn stereotypes, behaviors, dislikes, and appropriateness, by mimicking what they see and having their brain stimulated by what they come into contact with. So if they were exposed to things that made them feel like the whole realm was meant for boys, and if everyone felt that was "right" when they actually came into contact with it (basically if peoples brains actually were already programmed to listen to the massly broadcasted mind control messages fed by media, corporations, and blah, blah), they would basically believe that and fall into the molds.
Now schools and stuff play a roll, too. So if in early childhood, and early life experiences, there gender differences were programmed, each person would naturally in their own mind tend to follow the paths that were seemingly appropriate, laid out for them, and all that. What's worse is each person would physically follow this and believe it, and continue the pattern and practice of discussing, feeling, and seeing the world through these narrow means, because they themselves had been programmed to think and follow and know only that. The way the brain works of course, are the ideas, conceptions, things people see, hear, all that, images and sound broadcast into the mind through TV and radio, stereotyping or even just joking and satire, all this shapes the mind because stimulation like this makes those brain regions more dominant, it basically molds their personality and perceptions and behaviors, no one can actually escape it. This is why seeding healthy messages early is important, but in a capitalistic society where things are only done for profit rather than for best outcome, this isn't happening. Also military and government like us to be retarded, there are ties to early mind control tactics developed by the CIA, Disney, and others, that essentially help to control society and make it more profitable and more of what it is today. Meaning, the flaws we have, those are all by design, it's deliberate, they created it all entirely..
What we have today is a society, people, and system, set up to make us follow our leaders, and that includes gender rolls and other shit, making the girls girls, boys boys, and all sorts of other problems (The CIA/Military also likes a more aggressive crop of people, it's that sophisticated, they are doing this..)...
They also love people to be thrown off, manageable, and chasing the white rabbit their whole lives, never able to get the big picture, avoiding any sort of ricing up / independent thinking that might lead to disobedience.. (think back to the Cypher character in The Matrix movie. See how he'd rather have a nice juicy steak, than to have his freedom? Typical American, unwilling to go against anything wrong, including the man that might cut off his paycheck and access to a steak. The American government also set up a distribution network of steak, to keep the supply coming, for those who accept the program.) :D