Seems no one wants to go to the tire Manufacturers site and find out what each one recommends.
In my experience it varies greatly from compound to compound and to suggest that there is one rule for every tire may be wishful thinking.
The old thumb nail test was at one time a reliable guide - if the rubber was soft enough that you could leave an impression with your thumb nail in the tread tire life was going to be measured in months, not years.
Five years is now suggested by some manufacturers as the maximum age for their tires, with the rider that if there is any sign of cracking on the sidewalls they should be replaced sooner.
There is a old theory that if you store tires in the darkness for a few years they will harden up and last longer.
If true grip would probably decrease by a similar amount, and today there is not a lot of need today anyway.
The compound on used by people like Michelin for their Anekee's seems to combine exceptional grip with long life, and taking the life into consideration they end up being much cheaper than the low ticket , short life tire.