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 ;D