Year and a half is no big deal. Think about the leftover new bikes that are sold. Think about some of the low mileage used bikes being sold on this forum. Bikes bought new in 2013-2014 and only 3-4,000 miles. Unless your one of them. Just another thought, if you happen to get a tire that is 6-9 months old, YOU my be that person that discovers an defective batch of tires, the bad way. I generally use 1+ front and 2 rears a season.