Much fuss is made about "old" tires these days, but in reality there is no fixed, age-specific expiration date for a tire. This will have as much (or more) to do with usage practices, operational climate and storage conditions than it will with simple age. For example, a 7 year old tire that has seen chronic underinflation, lots of aggressive/high speed usage and exposure to excessive heat and sunlight will be far more structurally deteriorated than a similarly aged tire which has seen none of these harsh conditions. The recommended replacement intervals from the tire industry likely look at typical worst case scenarios for liability reasons, but these may or may not apply (too soon OR too late) for applications used well outside the "typical" situation. On my garage queens I have tires that are 9 and 13 years old with no current plans to replace them; on the other hand, for a competition vehicle even 6 years might be too long. Somewhere in the 6-8 year range is probably about right for the average daily driver, and that's typically been the recommendation of the tire industry in recent years.
Having said that, if you didn't buy the tires new yourself then you can't really know what sort of life they've lived, so replacement at the earlier end of the spectrum is probably not a bad idea.