I'll refuse delivery on new tires manufactured more than 6 months ago.
I bout 18 slicks for my race car once; they were cheap and 3 years old); I figured they would last me the season. I mounted four and they didn't stick; street tires were grippier. I threw away the other 14 tires and bought me some fresh rubber.
The tread compound starts to seriously deteriorate after 3 years of the manufacturing date; it turns very hard and unsticky.
I am in the habit of replacing tires every two years, regardless of tread depth. Tires are so important that you shouldn't even think of quacking around with them; if your tires don't work, then nothing else does either.