The question came to mind, if you've never sailed, why are you planning on retiring on a big catamaran? Why not a monohull, or why even a sailboat at all? But that's your business, of course!
When I buy a boat (and I've bought a lot of sailboats over the years) I ask the seller to rig it with me on the trailer before I buy it. That way (A) I learn how to rig it, and (B) I can look for missing or damaged parts. If at all possible, hoist the sail (face the trailer into the wind) so you check the halyard and mainsheet hook up. Include the rudders, tiller, etc so you can check them out in position.
I don't know the Wave at all, so I don't know if it has outhaul, downhaul/cunningham, vang or any of the other variations in rigging. BUT, you can get a copy of the Wave assembly manual from this site, print it out, and compare it to the boat as rigged. Here's a link to the manual: http://www.hobiecat.com/support/wave/
I know there are a couple of different versions of the Wave that have a different trampoline arrangement. I don't know the details, but I'm sure the Wave owners can help you with that.
From the photo, I would say it's a good deal. Boat has the backrests which are nice. Hulls don't have any obvious problems from the photo. Like previous people have said, hull damage is a deal breaker on a roto-molded boat. Fiberglass boats can be fixed, but not roto-molded, at least not easily and reliably. Mainsails are expensive, so look it over for tears. Mildew won't be a problem down there. Trampolines aren't expensive. You can buy Hobie or aftermarket. I lean towards Hobie factory parts in most cases, they are superior. But you can find them on eBay for around $250.
Personally, I would plan on replacing the shrouds (side and forestays). I had a side shroud break on a used boat and was dismasted. The seller said the shrouds were recently replaced, obviously they weren't. A shroud set on eBay for the Wave is $100. Cheap insurance. Also on eBay currently is a 2010 Hobie Wave for $3900.
I've had 2 Hobie 17s. They are solo racers. By yourself, it's great. If you and your wife are medium sized or small, it's Ok for the two of you. 3 Adults? Forget it. It'll be submerged. Length on a Hobie doesn't determine how "big" it is, i.e., its carrying capacity. I bought the 17 in the belief that it would carry passengers better than the 16, and an unscrupulous dealer let me believe that. I would have been better served with a Hobie 16.
I don't know how the Wave is for 3 adults, again, the Wave owners can help you out. There are a number of potential trouble areas on the 17; notice that I now own a Hobie Getaway instead of a Hobie 17. The Getaway is more like a really big Wave: simple, reliable, rugged. For my first sailboat, I would NOT buy a used Hobie 17. My first sailboat was a brand new Hobie 17, some years later I bought a used Hobie 17. I know that boat really well, and I still ended up with a boat with a lot of problems (that was the boat that dismasted, and that wasn't even the most serious problem I had with that boat.)
For a first boat, I think the Wave is great. If the hulls and mainsail are OK, I would get that one. Everything else is replaceable at a reasonable price. The price is right, and heck, he might come down a bit. Like I said in the beginning, have him rig it and check it out. Then go have fun!