What is the oldest written source in this country that mentions this right?
United States
Freedom of the press is protected under the First Amendment of the US Constitution: “Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances" (Constitution Annotated, "First Amendment").