 There's a reason some boys are aggressive while others at the same age are not. I'm Cooper Lawrence, health and wellness expert, and this is all well and good. Two 13-year-old boys are in the same class. One is inexplicably aggressive while the other isn't. Psychologists thought it could be an innate personality trait, but a new study from NYU found otherwise. One is they tend to be from families who have mapped out what it means to be a man or have masculinity. The second is that they perceive a non-confrontational situation as a threat to their manhood.