Wiktionary
n. (context publishing English) A person employed to carry copy and run errands.
Wikipedia
A copy boy is a typically young and junior worker on a newspaper.
The job involves taking typed stories from one section of a newspaper to another.
Reporters typed their stories on slips of butcher's paper...then a copy boy ran the story into the neighbouring subs' room, hence the cry of 'copy'. Each slip of the story had about six carbon copies...stapled together and it was the job of the copy boy - or girl - to separate the original and run it to the subs, and then separate the carbons for distribution. (from Guthrie, 2010).
Usage examples of "copy boy".
For my principal duties as copy boy, phone-answerer, coffee-procurer and occasional typist, I was paid four dollars a week.
Wynand filled in as city editor, managing editor, wire man, rewrite man, copy boy.
But he had a certain style -- 'the trouble with this film is that it goes on long after it has finished', he wrote -- and so the editor offered him a job as a copy boy.
He got his degree at some night school on Post Street in San Francisco, while working as a copy boy for the Hearst Examiner.
Ken had been at The Saltire for nearly forty years, from a fourteen-year-old copy boy to news editor, a position he had held - more or less - for over a decade.
John Welter began his writing career as a newspaper copy boy, buying cigarettes for the city editor.
If you'll just remain where you are, a copy boy will be down with everything within the next few minutes.