'Teen Film'
The 1950s is probably where teenage subculture was born--it is when Rock & Roll was on the rise and generational values were clashing, all naturally coinciding with the first movies to show life through a 'teenaged' perspective. Seems music still had a bigger market during the 50s, as after "Rebel Without a Cause", I can only recall 1959's "Gidget" as the an example of a major teen film. But 'Rebel' strikes me as the first significant example of a movie in this style, or in other words, the earliest inspiration for the teen film market. Shortly before that there was Brando's "The Wild One", a movie that had a profound influence on youth trends and even reputedly on how James Dean modelled himself.
Is it safe to consider Rebel, or The Wild One, to be the first teen film? Are there others I'm missing?