Stemming from See you in later days
Thought to have originated from "The Weekenders", but was actually seen in a 1984 pic about punks in suburbia, named Suburbia
Joe - "Later Days
Used to indicate that you will see the person later.
From "The Weekenders," a cartoon show where the main character would say it at the end of every show.
Dude B - "Gotcha man, later days."
This term was made famous following the suicide of 16yo Jeremy Wade Delle in 1991, after passing a note to a fellow classmate he signed the note "Later days" rather than his usual "Write back". This suicide was the basis for the song Jeremy by Pearl Jam.
"Yeah, later days"
"Later days" was a term used like "dude." Depending on the inflection in your voice, it could mean several things.
It could mean everything from "i"ll see you tomorrow," to "if I ever see you again, I will kill you."
In SoCal, the term eventually shortened down to "later on."
This became a generic term for, "see you later." It lost most of its inflection power at this point.
Probably a year later or so, (the time it takes for slang to morph) the term shortened down to "later."
It lost all inflection and became a simple goodbye.