How long do speakers last?

What kind if speakers are they?

If they are exposed to direct sunlight it can damage the rubber or foam surround and or if not kept in dry storage can reduce their life expectancy. Otherwise they can last for a very long time.

Actually if your speakers have foam surrounds they could have rotted by now. You should inspect them because if you run them without the surround much you can damage the voice coils. New surrounds are cheap and easy to replace. Once done the speaker is as good as new. I'm presently listening to a pair of Dynaco A 25's that were made in the early seventies. Rubber surrounds so no rot. They work fine and sound pretty good too.

These are dcm time windows. (not sure model)

As was stated above it depends mainly on the surrounds. If foam then less than 10 years same for butyl rubber and the like. I inherited some 1959 JBLs which work fine, however they use fabric surrounds and compression horns. You need to take that sock off unless some one knows what type of surrounds you have. Most used foam or rubber by then. Therefore I would recommend getting them remounted.