Green’s Dictionary of Slang

writing, esp. office work; thus push a pencil v., to perform office work.

1889		Salt Lake Herald (UT) 3 Feb. 3/2: After several months of indefatiguable pencil pishing for the Utah Daily Union professor Leo. Hoefeli announces his retirement.
1894		Marble Hill Press (MO) 31 May 8/5: In the absence of the editor [...] the foreman is trying his hand at pencil-pushing.
1903		Goodwin’s Wkly (Salt Lake City, UT) 19 Sept. 5/1: We pencil-pushing league of rogues [...] engristed in the journalistic mill.
1914		Dab Book (Chicago) 29 May 5/2: There will be no pushing except a little pencil pushing now and then.
1915		G. Bronson-Howard God’s Man 193: You’re back to pencil-pushing now?
1981		M. Baker Nam (1982) 16: What’d you do in college, boy? Learn to push a pencil?