I have a knife that was my grandfathers and maybe even passed down to him, so it has to be 40 years old or more. Has real bone on the handles. I have my great great grandfathers rifle, though it wasn't taken care of so its not in a condition to use it, its over 100 years old, I'd say either a gun or knife would survive provided it was cleaned and oiled before being put away.

WRT computers, tell them your characters father was an older engineer and had an HP calculator sitting around an HP48 or 28 or so, those will last 40 years, mine is 20 years old. They are basically a computer, 4 bit cpu and can be programmed in machine language exactly like early computers.