His father brought him to Afghanistan to fight and not to play video games or attend high school like your typical Canadian 15 year old. What if he had shot a Canadian soldier? Would you still feel the same? 

I challenge anyone to go visit Afghanistan and go tell a local 15 year old that he is a child. The reaction should be interesting and, depending where you are,  might possibly be fatal. Consider that the average life expectancy is 44 and if you are not married by the age of 18, you are considered a social outcast. 

Applying first world values to a  basically tribal if not medieval society is borderline colonialism. It fits in perfectly with Al Qaeda's philosophy.