It really depends on the speakers. Foam surrounds can rot after 20 years or so.
Mine have butyl surrounds and are 35 years old. 5 years ago I refreshed the ferro fluid in the tweeters. They’re as good as new...maybe better because the caps and woofers have thousands of hours on them. Hoping to get another 30 years from them.
It’s a good practice to rotate your woofers 180 degrees every decade or so to offset for any gravity pull.