Nobody worried about "teenagers" prior to the 1940s. In fact, as a culturally or economically defined entity they did not exist. But in the 50 years since the last world war, when the term was first coined, teenagers have had an enormous impact on American culture. They have reshaped our language, our music, our clothes. They have changed forever the way we respond to authority. They have become a 200 billion consumer group avidly courted by marketers...