They CAN cause them, but mostly don't. It's true, teenagers are impressionable. It's true, video games are really violent, but honestly, take a look at history. This facade of "peace" is neither usual nor lasting from an historical point of view. Several generations have had their young ones assaulted by, not war games, but REAL ACTUAL HONEST-TO-GOD war, and the human race is still here to prove they successfully grew old and multiplied.
As for the normal point of view, usually a teenager who is prone to delusions will be affected by violent games, and usually a teenager who is not, will not.