Good catch.
There are two reasons that I pick S.E. Hinton as kind of the beginning of the whole greaser thing:
The first is that she uses the term "greaser" explicitly without references to Italians, Mexicans, or Puerto Ricans. If you go back to that period, that was rare. Indeed, when Sha Na Na were reinventing the Fifties in the year or two
after The Outsiders, they were worried that their references to "grease" and "greasers" might be interpreted as insensitive to Italians. Hinton, Sha Na Na, and Jacobs & Casey (the creators of
Grease) all took the term "greaser" and emptied it of its
ethnic connotations (at least partially).
The second is that she consciously deals with the idea that a golden age is passing. In
The Outsiders, it's a personal and intimate thing (consider the use of Robert Frost's "Nothing Gold Can Stay" and the classic line, "Stay gold, ponyboy."), but it's there, and it flows through her work as a whole. (Take a look at
That Was Then, This Is Now--chronologically, it follows pretty close on the heels of
The Outsiders and while the main characters' lives intersect with the lives of some of those from the earlier novel, but it might as well be a completely different world.)
I've always thought that the "dead teenager" genre of songs (which "Leader of the Pack" is most definitely a part of) came from a very different place that had more to do with young people trying to navigate a radically different style of dating. I also think that the biker, proper, might be a different
type. I don't know. I'll have to think about this now that it's in front of me.
EtA: Oh, and to be clear, yes: I think that the "Fifties" ended right around 1963/1964. People seemed to recognize this intuitively, even without some kind of theory to guide them. "
Where were you in '62?" "Oh what a night /
Late December back in '63 / What a very special time for me" "
We now know the 1950s ended in 1963. The fall of '63 was the end of an era; new voices were being heard." Even so, in individual works, you get dates as early as 1959 and as late as 1965.