Hey Grandpa, I may weight a lot but I'm in better shape than you think. I don't eat fast food, or drink soda, and I cook/prepare most of my meals. My problem is that I've had a mostly inactive lifestyle since a near-fatal car accident 2 years ago when I lost an eye and had to have reconstructive surgery on my face.
Before my accident, I was a regular skiier/skydiver and did a fair amount of mountain biking, and still could not drop below 230. I am now walking regularly, playing frisbee golf, bike riding, and hiking occasionally.
My skydiving experience has taught me well to avoid activities that I am not prepared for, and to seek the advice of others in regards to technique and safety. Believe me when I say that my swimming and paddle strength are not a concern on the types of runs that I would be boating on.
You would do well to make sure you're hungry before you open a can of worms. I understand you think you're doing me a favor by trying to dissuade me from enjoying a potentially dangerous sport, but you definitely sound like a prick.