"Adaptable" vs. "flexible"

Are the words adaptable and flexible generally interchangeable? For example, do the following sentences have the same meaning?

Older workers are less adaptable [...].

Older workers are less flexible [...].

Those two phrases have meanings which are broadly the same but not identical. Adaptable indicates long-term changes; flexible more short-term alterations. One might adapt to the introduction of a new shift pattern, and be flexible enough to work late next Tuesday.

But adaptable and flexible are generally not interchangeable: the former means "able to be adapted" (or possibly "able to adapt"), and the latter "able to flex or bend". To describe an adaptable building as flexible could conjure up an alarming image!

That said, a building might be adaptable enough to accommodate a warehouse or a school (a long-term use), or flexible enough to vary the number of rooms by having easily-moved internal walls (a shorter-term change).

From an engineering point of view, I wish to dispute Andrew's concept "Adaptable indicates long-term changes; flexible more short-term alterations" .

Flexible is to provide inherent usability across a wide and changing spectrum of deployment situations, often without making significant or any changes to itself.

The weapons are flexible to be deployed to either the Arctic, Iraq or Afghanistan. There is no modification necessary, except that, we have to make a slight permanent and long term modification to the trigger. And soldiers have to make a short term adjustment to the way they transport it.

Adaptable is to be inherently modifiable to be deployed across diverse situations of deployment.

The weapons are quickly adapted to being used in either the Arctic, Iraq or Afghanistan. The necessary modifications are quick but complex. They are not permanent changes to the weapon. Once a weapon has been adapted for the first time, soldiers would need to make a long term adjustment to the way they transport it.