How about Goethe? His The Sorrows of Young Werther was the first work of art to market self-pity to teenage boys. But he didn’t have screaming girls mobbing him. For that you need mass communications.
The biggest early star was arguably silent movie idol Rudolph Valentino (1895–1926). The funeral in New York following his untimely death saw 100,000 people take to the streets, and several of his female fans allegedly committed suicide.
You can make the case for other movie stars – matinee idols – but the first major celebrity with an identifiably teenage following was Frank Sinatra, whose appearances in the 1940s were characterised by screaming ‘bobby soxers’.
The 1950s saw the real rise of teen idols because teenagers now had money to spend. Rock ’n’ roll happened because there was a market for it. For British idols, let’s not forget the huge appeal of Dirk Bogarde in the 50s, though our earliest homegrown rock star was Tommy Steele. He was rapidly followed by several young men with new names contrived by impresario Larry Parnes, including Marty Wilde, Billy Fury and Georgie Fame.