In principle programs shouldn't stop working just because they are old.

Yes, no language completely realize this. But there's a world of difference between C's "it was written only 40 years ago, why did compilers break it?" to Python's "yes, you are expected to review your code every 3 or 4 years", and there is another world of difference to the faster Javascript frameworks that practice "your code is 6 weeks too old, your looser!"