Some theorists (Bandura) believe that aggressive behaviour is learned and maintained through environmental experiences.
Aggression which is learned as a way of solving issues and conflicts are normally learned at a young age and is considered normal behaviour around the age of 8 years old.
Aggressive behaviour is learned in all kinds of places including the classroom, schools, peer groups, family and community. When discussing community, we are looking at inner-cities where minority children may be vulnerable to displaying anti-social behaviour due to extreme environmental conditions they live in.
However, the person who is most likely to behave in an aggressive manner, is the one who is programmed to respond in that way due to previous experience and learning. Experience can be observing not necessarily acting it out themselves (e.g. watching lots of violence on screen)