lol I bet the sisters are like Astagfirullah, are all little 13 yr old boys in America violent?
Well yes, they are. And it also starts from age 10. and it depends wher you get your motivation from.
Bad peers, bad school (AHEM, Kafir ones in exact), then yeah, you'll learn and know all the bad stuff.
Like how to go jump into the fray during a fight; I'd only do that if my friends wouldn't be able to handle it all to themselves, and if they could, then I'd leave it to them to take the honor of winning the fight.