Kleppers have wooden parts, not aluminum, so that in itself is no indicator of age. A Klepper frame, if reasonably well maintained, will outlast 2 or 3 hulls.
It is not that hard to assemble with a little practice. If you don't have the instructions, a Klepper dealer or Klepper America should have them. It does look complicated, but it's really fairly straightforward. I can put my Klepper double together in under a half hour without rushing. However it should be OK to store and cartop assembled. I would let the air out of the sponsons for storage, but probably inflate them for transport to make it more rigid. I can't think of anything that would be damaged by leaving it assembled, but I don't, so I can't give a definitve answer from personal experience.
Ralph Diaz is the US guru on folding boats, publishes a newsletter on them, and is active on the web. I don't have an address for him, but a little searching should turn it up, and he would be able to give you more authoritative answers to your questions.
Of course if you really have no use for the boat I can think of a good home...
The phrase "Too many kayaks" is an oxymoron.