There is a local (not sure if Fed or Prov law) that tire shops can't repair a tire over ten years old. I found that out last year with the 1991 C we got that later had a nail in a back tire episode. They would not even use my spare, saying it was over ten. Had to get four new tires at the back (my choice instead of just one new one)
IMO a certain amount of common sense should apply rather than a dogmatic replace at 5 years. Those guys that put bags over their tires when parked must be thinking that. (But having a bag over your ten + year old spare won't help around here unless you do the tire replacement job yourself :) )