There is a date code (you can Google how to decode it) on the tire that tells when it was manufactured. Lots of folks on this site say that 5 years is the maximum no matter how they may look.
IIRC, Discount Tire will not repair a tire that is 5 or more years old, but, of course, they sell tires so...
Sherm & Terry w/rescue Eydie (min Schnauzer) & Charley (std Poodle)
2015 Jay Flight 27RLS, GY Endurance (E), Days: 102 '15, 90 '16, 80 '17, 161 '18
2006 Ford F350 PSD, 4WD, CC, LB, SRW, Cmpr. pkg, Equal-i-zer 4-p, ContiTrac TR
Full timing: Some will think you're crazy, some will be envious, just enjoy the freedom!