There's a lot information and opinions that get thrown around with regards to tire age.
Most of the issue is heat related. This is a very prominant in Arizona - where the summer tempatures are extremely high - and Florida, where the temperatures are not as high as AZ, but it's warm year round. In these locales 6 years is sometimes a not so conservative number. But in Winnepeg, 10 years is a good value.
Also, tires don't age much before they are put into service. Again, it's a heat issue and you don't generate much heat unless the vehicle is moving.
It has been said that unused tires within 3 years of the date of manufacture are - for practical purposes - the same as yesterday's made tires. The except is if the tires are not stored properly.
It is common practice for tire manufacturers it gradually reduce the selling price of older batches of tires with the idea they will sell more quickly and the age problem will take care of itself. While many retailers won't tell you why there's such a bargain on a giving set of tires (and many are not even aware), do not be surprised if your bargain tires are a little older.