Music not only "affects" teenagers but can begin to define them of people and delineate them from others. The type of music you like becomes a critical factor by which the person retains identity. Music becomes the dictator of what clothes you wear, what people you associate with, what people you will hate, sometimes what political and or moral beliefs you will have.
Take for instance people who listen to rap predominantly. Such people will begin to dress in a certain "gangsta" fashion. They will often speak ebonics regardless of the fact that they might be rich white kids.
Or perhaps take for instance a person who listens to Nazi Skinhead music. That person will wear particularly clothing identifying them as a skinhead. They will be attracted to the politics of National Socialism. Obviously, their hairstyle will be a lack there of.
A person who listens to Goth music might wear all black, paint their finger nails black, enjoy walking in cemetaries, pretend to be a witch or warlock, and act jaded.
A dude who listens to metal will largely be defined by the type of metal he or she enjoys most. For instance, an individual into Black Metal will be attracted to Satanism, Occult Mysticism, religious fanaticism, and often times Norse or Classical Paganism. He might be attracted to the politics of Tyranny, Imperialism, Aristocracy, & Feudalism. He might read the works of Arthur Schopenhauer. He will wear live ammunition around his waist and own either firearms or medieval weapons, or both. He will either have long hair or a shaved head.