Tires: Age life of tires, vw cabrio, cold climate

Question
My wife has a 2001 VW Cabrio.
When not in use, it is parked in the garage - not exposed to a lot of UV, and we live on the Coast in British Columbia. Tire pressures are checked every 2 - 3 months. Usually there is little to no change in pressure.
She drives about 6000 klms a year. The tires are all season and still have good tread.
What is the usual age limit for tires under these conditions

Answer
Ron,

Recent bulletins from the tire industry indicate that tires degrade simply due to time.  The age of a tire is important even if the tire is unused.  There some disagreement over how to best express this age limitation, but my take is:

If you live in a hot climate (AZ, CA, NV, TX, and FL) then the limit is six years.  If you live in a cold climate (MN, ND, WI, MT, etc), then the limit is 10 years.  States in between are  ..... ah ........ in between.