CS,
I got the 9 ft( 274+ cm) length from an Internet search about paddling a canoe with a double paddle. You need the extra length for canoe, even a solo being wider than a kayak?
I'm using it in a 16 ft SR tandem, paddling backward from the front seat.
One year when I was with another guy, I got the "bright" idea to bring a cheap 8 ft kayak paddle I bought at garage sale to see how it worked.
I was the stern guy. Even with me being 5'9" and normal length arms, I was constantly banging the gunwales, unless I used the high angle paddle.
My Internet search talked about that, and recommended for a tandem paddle solo, or a TRUE solo canoe, the 9 ft was the way to go.
Your sitting much higher in a canoe, even if you kneel to paddle. However your pretty tall, and with your long arms, it might or might not be the right length for you?
I researched kayak strokes as I knew nothing about them. From what I could find, the best stroke for me and my steady endurance style of tripping, was the low angle, or what I call the touring stroke.
As others have mentioned, a double is harder on you physically. If you can't paddle steady for an extended time with a single paddle at a decent clip, you won't do very well with a double.
But the good news is that your ONLY 36 Just a baby! I'm 60, and have ZERO shoulder problems. If you do the work, push-ups/inverted push-ups (feet on step/chair, dips for triceps, Lateral raises for shoulders, one arm rows, things for upper back and shoulders, plus some CORE work, you should be fine. The first long day I used double paddle, it wasn't my shoulders/upper back or arms that were sore the next day, it was my abs/and hip region! When your in a steady rhythm in the TOURING stroke, your using your abs and hips to help power the stroke on each side. I set my packs, so they act as a foot brace, this will allow you to get more power in your stroke. I found that unless your going into a stiff headwind, you don't have to "dig" your paddle blades in that hard. Sort of like peddling in the right gear on a bike, a balance between stroke speed and "power". When you hit that "sweet spot", you feel like your hardly working, yet your moving along at a good clip. You don't want to exaggerate the extended motion with your arms. Never LOCK your arms out at the end of a stroke, it just hurts your elbow joint.
If you can find a place on the water that sells kayak paddles, you should be able to try different ones, and find the right length for you. I'm guessing the kayak guys have some kind of "formula" for figuring paddle length to boat width and paddler size?
 After all that, you may decide the double ISN'T for you, but you don't know till you try
If it works out, there's a guy on here that might make you a good deal on a nice carbon fiber paddle

C_S,

My double was made by/for Mohawk Canoes, and was sold as a double CANOE paddle, not a Kayak Paddle for canoes. They still make Mohawk canoes, but don't know if the still sell paddles?
It's 9 ft, tip to tip. Mine is aircraft aluminum, with a plastic paddle.
The paddle tip is similar to the aluminum type paddles you'd use on whitewater river paddling.
It's very stiff, no noticeable flex in shaft, but obviously heavier than a single paddle or a upscale kayak paddle, that has the tapers type paddle blade and graphite shaft. It can be set for a feathered or conventional angle.
I wanted something affordable and rugged, this filled the bill.
I double portage, heaviest pack and day pack first, then lightest pack and canoe. I use the double paddle as a 3rd leg when needed. It's saved me from falling many a time. In camp, I even used as 2 fly poles for my tarp, when the tree selection was farther away than I liked. End of trip, I have to smooth out any nicks or cuts in blade, and maybe put a bevel on the edge. For $50 it can't be beat.
Of course being lighter is a big plus, but rugged counts for something too?
I just wouldn't spend a bundle, until you KNOW the double paddle is for you?
  280cm between blades plus another 2 ft or so of blade would be about 11 ft or so overall. The 240cm shaft measure, plus blades is closer to the 9 ft OVERALL that I use. Just for the heck if it, measure the 240cm, tip to tip? Should be pretty close

FWIW,
I paddle a Bell Magic. I use a Bending Branches bent shaft, and I won't leave home without it. I feel comfortable with it on lakes, streams, calm or choppy. I appreciate the tradition. (I also use a traditional Duluth pack.) That said, a couple years ago I was enticed by a kayak. Did the whole test paddle routine and finally made a purchase. I also spent some time with a very experienced yakker who taught me the do's & don'ts. Surprise, surprise...there is a proper technique for a double blade just as there is for a single. There's a learning curve, just as for the single. (I should mention that I have an 18 ft. touring kayak, not a 9 ft. plastic whitewater playboat) So when I started using the kayak paddle with my Magic, it didn't seem awkward.
I spent 8 days in Quetico this summer, and used the kayak paddle 90% of the time. I   was able to very easily keep pace with a tandem.
I guess the bottom line for me is: it is just like learning to use any other piece of equipment. Am I less of a traditionalist because I use a stove instead of a wood fire? A nylon tent instead of a canvas? Modern fabrics instead of wool? I  think not.
Give the double blade an honest effort. If you like it, use it. If you don't, abandon it.
Respect others' choices, but do what works best for you. And just have a good time!
Wind-in-Face
PS. Fishing is strictly a single blade job!! (At least for me)

Mostly I use the bentshaft as primary and a 9 foot double-blade as back-up (it also detaches into two pieces & doubles as the support structure for my lean-to style tenting arrangement).  If I'm in rough conditions, you can bet the bentshaft will be in my hands... not necessarily because it is better but rather due to confidence that comes with practice.  With more practice, I might feel more comfortable & secure with the double-blade in rough water.  We'll see.

On the other hand, if SPEED is desired & conditions are right, I'll make my time with the double-blade.  You feel like you're flying when you get the rhythm of both those blades going!  It's also a pretty good upper-body workout and takes some getting-used to.

If you are looking for an inexpensive, sturdy, two-piece double-blade option (not necessarily all that "light", however), you should check out Spring Creek Outfitters offerings (see: (You need to Login or Register to view media files and links); I went the cheap route just to get started & I'm pretty happy with my selection.

Good luck!

Jimbo