IMHO Bob Nester's comments nailed it.
The "aging factor" came in at about the same time as all other "out of date" B.S., i.e., milk, cereal, lunch meat, etc., etc., etc. IT IS A MARKETING GIMMICK, PURE AND SIMPLE. A lot of this started in the late '60s and early '70s, when every Sat. morning kids show commercials were filled with brainwashing on checking the expiration date and don't eat it one day later ! ! ! In our area now a mattress chain is stating "replace your mattress after 8 years" Gimme a break.
For the gospel on tires, visit the tire manufacturers' websites. Some, Michelin, Goodyear, Bridgestone, and others have excellent information on tires, including the aging factor.
You have to admit though, it sells a lot more product (and causes us to scrap a lot of perfectly good products.)
"In the tire industry 40 years; seen it all and done most of it"