The oldest computer mag I have is Byte magazine from November 1979. It was from a set that my uncle had and I kept this oldest number as a collectable, till today.

On Amiga side I have a September 1988 Commodore Amiga Revue the first Amiga magazine i found and bought.

In terms of publications I have several 1945 Reader's Digest, which are the oldest monthly magazines I have.