It's mostly wear and tear than age that determines if it may be close to death. Usually it just won't show up at all if dead, or give errors when trying to read/write from it.

It's odd that everything looks fine on the surface, but nothing is actually applied to it. I would say that this could be write protection causing this, but you would usually get a write protect error when formatting or saving to it.

As a test, see if you may be able to read/write to the SD on another PC, and see if you have any issues with a different SD on your PC.