Is 13 years too old for an otherwise new-condition tire? I was reading some product reviews for bike tires and came across a complaint from a customer who had received "new old stock" tires. Here's the relevant part of the review:


  
  
  Feb 07, 2020
  
  The two tires I received had the manufacture date stamp inside the
  tires of 2007 !!! THIRTEEN YEARS OLD RUBBER !!! ...  In reading these
  pages you have seen reviews stating premature blow-outs, and greatly
  diminished tire wear. Both are symptoms of OLD rubber. ... It would be
  a good bet that this supplier bought-out some distributors ‘old stock’
  for pennies-on-the-dollar. Let HIM eat his investment, not you. ...
  See the date stamp in the attached photo, both tires had the same
  stamp...


(source)

The review correctly states that other customers had complained about severe blowouts after relatively short miles, suggesting they too may have received tires too old to be reliable.

This seems plausible; but on the other hand I have some bikes with pretty old tires without problems. Of course riding conditions may also play a role.

In summary: is there a valid concern about otherwise new-condition tires that are 13 years old being unfit for use?



Note: I'm not asking for a judgement of this specific tire. It's just an example that prompted the question.
A 13-year-old tire may be rideable for a few years, but it wouldn't be fair to sell it as new. It just won't last as long as a new one would, and the hardened rubber will perform worse and possibly wear faster.

So, not necessarily "unfit for use", but definitely "unfit for sale as a new one". But depending on storage conditions and the tire, even a few years can make a tire unusable, such as obvious hardening or visible cracks.



As for the particular review linked in the question, it seems the buyer has misread the date code.

The page identifies the tires as Schwalbe Marathon HS. The Schwalbe Warranty Page has this photo of their production code:



The format appears to match the one in the question, but it still leaves at least two reasonable interpretations:


Day/Month/Year: giving dates of 20th July 2018 (question) and 26th September 2018 (warranty page).
Week/Year: giving dates of week 20, 2007 and week 26, 2009.


But, it appears that Schwalbe has changed their production code format with an extra digit in 2010 or so. Older sources, such as this recall from 2009 show a code that has only 5 digits before a letter:



Based on this, I'd say the format is Day/Month/Year and the date on the tire is 20th July 2018. It still makes the tires somewhat old to be sold as new, but not terribly so.