We had the same experience last summer in Washington state while visiting reletives. I noticed unusual wear on our front tires and decided to replace them. We went to a local tire dealer in Washington and they installed tires that were dated 18 months earlier. I didn't notice this until later after arriving at our home base in California. I did some research and found that this is very common and unless you specifly otherwise you will probably get tires that are anywhere from a year to even 4 or 5 years old.
