How long do good speakers last?

They should last longer than you do. I have a set (7) of 28 year old B&W 805’s. Sound great. On a couple of the subwoofers (I actually owned 4)  I had them “re-taped” after 20 years… that’s the connection of the cones to the frame.

Happily I bought set of new speakers when I was around your age. Then when around 60 I was able to upgrade to Olympica 3 before my retirement… and then in retirement to SF Amati Traditional. May you be as fortunate.

Depends on the climate.. here in Hawaii the foam surround lasts about 10 years if you are lucky.
In comparison, the Altec surrounds look brand new even after 50-70 years.

Years ago, replaced foam in Advents prob. 15 years old. Set of KLHs (very similar, no?) still going after 60 years in brutal conditions (summer home, deep frozen in winter). I did change the capacitors last year, just to do something, but I doubt they needed it. Current Focals sound (to me) exactly as they sounded when I got them a quarter-century ago.

(But, as implied above, even if the physical speaker lasts, the quality of sound relative to what other speakers are available will likely change; those Advents, which I loved, didn't sound so great once I found what might replace them).

Humidity plays a big role in how well speakers age.  We have a dehumidifier for the humid 7 months of the year and that keeps relative humidity to around 45%.  Moist enough that the seams don't dry and crack, but dry enough that mold doesn't grow and moisture doesn't destroy the cross-overs.

The oldest speakers I have are a pair of Polk Model 10 A's. 1979. Excellent speakers for their day. They still sound like they did in 1979. 
I'm skeptical of new technology that promises "better" sound. No one really knows how they'll hold up (or if the new company will survive to service your drivers down the road). There have been countless innovations that have turned into boat anchors. I stick with what is tried and true.