Buying used: how old is too old?

Looking at a pro/studio speaker manufacturer like ATC they’re pretty much unchanged and cut from the same piece of cloth for more than 4 decades now, the most noteworthy changes being their newer, self-developed tweeter design, the Super Linear magnets, and some minor aesthetic changes (i.e.: no sonic impact here). If anything they’ve been a constant more or less for almost half a century and an unwavering marker for others to be measured against, during which time they haven’t gone from being the frontrunners over all other speaker brands to being a bland, outdated product overtaken by more "modern" designs (with their ever changing design revisions and new models). No, ATC is doing just fine and being a reference still for many, not least with their active iterations, a clear indication that when done right from the outset a design, at its fundamentals, will retain its pedigree for decades. That’s not necessarily to say a segment of audiophile-aimed "Hi-Fi" speakers haven’t evolved these last decades, but I’d wager this predominantly domestic part of speakers have for the most time worked from compromised outsets confronted with all sorts of restrictive aspects, and therein lies the real challenges to be faced.

A few months ago I listened to a pair of decades old, actively configured all-horn British cinema speakers, and anyone with a pair of ears on their head and some ability to honestly, openly and without prejudice discern listening impressions would be able to realize that this stuff plays music in ways that most domestic speakers simply can’t approach. No, it’s not really about volume only, dynamics only, presence only, ease, resolving capabilities, envelopment, engagement and other isolated, singular aspects, but an overall sensation of being presented to and immersed with music re-vitalized. You’d have to take my word for it, but it’s a fact if ever there was any. And yet in this business we’re to believe the wheel is constantly re-invented, when what’s at the basis of all is missed by many, if not most.

@bjw54   I have a 28 year old pair of Legacy Focus speakers that look like new and sound better then new. These are now in a primary system that costs about $70,000 in a $160,000 room.  I intend to upgrade to a $35,000 to $50,000 speaker (used Von Schweikert or Evolution Acoustics)  As to the Legacy Signature IIIs in my living room (and eventually will be added to my video rooms when I find more of them under $2,000) I love them so much I will doubt I will ever sell them.   I used your quotes because I agree so much.   I had to replace the deteriorated foam Sig III bottom woofer surrounds only (the other two have durable rubber surrounds).  

Speakers do not wear out i have some 73 year old speakers that happen to be the best ones that i own of my many pairs so if they are a quality speaker do not be afraid of the old ones especially if you have a professional type driver in them.

I think it depends on the speaker. I had some ESS AMT 1Ds that had the cones disintegrate after about 15 years. I have had my 2 of my 20 year old 4 B&W 800 “retaped”.  Some of the older speakers may have been made out of material that may not hold up… some appearent ly does.