I suspect it relates to both age and race. Young men make me nervous, to be honest. I think it relates back to the fact that the people who inflicted random physical abuse onto me were young men. Not that I have a history of physical abuse or anything, but you know... Some people on the school yard (or even the street) can be really ♥♥♥♥ed up.
I think what you said about race is normal, and you are right, we would benefit by examining our unconscious prejudices. One of the moments in my life that I am ashamed of is when I blatantly turned my back on some young Aboriginal man that was asking for my help because I was afraid of him. He looked incredibly hurt while I was turning away.
I think there are structural reasons for why we developed a certain stereotype around groups of people. In Edmonton, the majority of gang members are Aboriginal, which stems back to poverty, which in turn, stems back to historical colonialism. Regardless, the majority of murders that take place in our city our gang related. I think a lot of people, including my self, just have a knee-jerk reaction of fear when they run into a young Aboriginal man. It is an incredibly insensitive thing to do, but yah... it is there.
I think, Mariana, you were taking more of a cultural studies perspective? Cultural studies isn't really one of my strong points. I do remember a class discussion asking whether parodying racist stereotypes serves to reinforce or deconstruct those stereotypes. We were watching some Weird Al video where the black men were portrayed as stereotypical gangsters that wanted to threaten Al.
It was meant to be funny, but yah... it is still reinforcing a stereotype. I'm not sure what to think about it, to be honest.