How long do speakers last?

As others have said here, the big question is the bass driver surrounds.  Are they foam or rubber?  The foam surrounds can be counted on to hold up for 10 years and often longer.  But not that much longer.

Purchased the Altec Lansing A7-8 VOT speakers in 1974, outside of refreshing the cabinets the drivers, crossovers and horns have never been touched. Kept out of direct sunlight and never abused. 

My Acoustat Spectra 33's were built in 1988. 35 years old. I had the interfaces rebuilt last year, but the panels seem indestructible. I had the interfaces rebuilt as an upgrade, not because they weren't working . 

Enjoy the Music 

I have an RCA Photophone Shearer horn that has original drivers from 1938 it still sings and amazes even jaded audio designers. I have a lot of drivers and speakers from the 1940s to the early 1970s that are all matching specs. It depends on the build modern loudspeakers with their polymers and ferrofluids do not last that long figure 15-20 years most would need service before that time frame. Sure they may play but the fluids dried up in VC and the modern plastics break down capacitor values may also have shifted with age thus not meeting specs  

I bought my Kappa 7's off the sales floor (last pair in store) in 1990. 3 wives, 2 kids, 5 houses, 2 dogs, dozen cats, 4 integrated amps, 2 TT, 1/2 dozen tape decks, more cd players than I can count, 3 re foams later, and they are still my daily drivers.