(Mr Lane's Note - This is a long post; please don't forget to click 'read more' to see all the detail (and clips) for the different youth generations. )
Jon Savage's book (and documentary) establishes that although the idea of adolescence being a separate state from childhood and adulthood begins to exist in the 18th Century, with children working in the industrial revolution, the term 'Teenager' as a concept, as a collective identity, doesn't exist until 1945 and the end of the second world war. Savage defines a teenager as between 13-24 years old.
Click below for more details