When people say girls are not good at maths I get wild!
but when people say most of the criminal/terrorist and socially disruptive are young males. I nod and agree
Am I sexist?
just like I am good at maths A,S and V are perfectly sane and not prone to aggression/criminal-terrorist activity :D . Why dont I object to the second meme?

answer: Thats because they are not stereotyping young men as aggressive, they are stereotyping agressive people as young men. Got it? 
Its like saying all those who didnt do well in maths are girls, that's  different from saying all girls are bad at maths.