There have been a number of discussions about tire age on another bike website I frequent. Since a number of mfrs say a tire stored under proper conditions is good for 10 years or more from date of mfr, many of those guys have said a 6 yr old tire that will be used up in one season is not an issue. Many of these guys are high mileage sport touring riders. I counter, how do I know the conditions of storage were optimal?
That said, when I got a 3 yr old tire (that would likely last me 2 to 3 years) and said I would return it, I got a lot of 'just send it to me' responses. In the end, what matters is your confidence in the hardware under you. Btw, Revzilla matched the lower price (from that other vendor) and shipped me a replacement that was less than a year old (this was about 5 or 6 yrs ago).