So much depends on design and whether direct sunlight falls on exposed drivers. As others have mentioned rubber surrounds can go bad quickly. By that I mean that surrounds can become brittle and start to tear or crumble when speakers are as young as 15 years or so. Pleated fabric or paper surrounds can last a very long time. I've heard woofers that are 90 years old that are still good Horn compression drivers can last a VERY long time I own a pair of compression drivers that are over 80 years old. Tweeters can last a long time without any maintenance if they don't have ferro-fluid in their magnetic gaps. That stuff can start to dry out as early as 15 years or so and maintenance requires taking the speaker apart to clean out the old stuff and replace it with new ferrofluid.
Crossover components life really depends on they type of capaictor used. If the crossover employs modern film caps or ancient paper in oil caps, they lifetime can be extremely long. I am having a crossover made which will be using paper in oil caps that are 60-70 years old. Electrolytic caps might not last long, but, it depends a lot on the make of the cap.
