But it dates back to at least '96. That's 1696.
According to Slate,
In 1696, British publisher Ichabod Dawks left blank space in his pages for readers to supplement the words he printed. The first edition of Dawks's News Letter, dated Aug. 4, 1696, told readers, "This letter will be done upon good writing-paper, and blank spaces left that any gentleman may write his own private business."
And it spread to the colonies:
....the Boston News-Letter, first published in 1704. Its proprietor, John Campbell, deliberately left blank space in its pages so subscribers could annotate and otherwise append their ideas and "news" to the newspaper. These amendments weren't aimless jottings, either. Newspapers were routinely shared after purchase, and the notes readers added in the spaces and margins were designed to edify the friend or acquaintance the reader next forwarded his paper to.
Makes me wonder if this continued throughout the 18th century, and what impact it had on the American Revolution....
And makes me think that Ichabod needs to be a little better known, he's not even mentioned in wikipedia!