@edgarblythe,
I wonder about that bone density thing. I'm 82 now, but 5 years ago I was walking at night and blundered off a creek bank falling head first onto the creek bed. The bank was only about four and a half feet above the bed, so it wasn't that high. The fall changed the shape of my shoulder a bit, and I hurt for about 3 weeks, but otherwise it was all right.
I read about how older people are supposed to be careful about falling, but I hike everyday in the wild area and I trip and fall occasionally and don't worry about it. Maybe my bones are stronger and denser, I don't know, but I'm a pretty decent swimmer, and I love being in the water. When I was a teenager, I taught myself how to swim using the dog paddle. It all starts from there. I never use the front crawl, which swimming schools seem to think is important. It's important if you're swimming long distance, like from Cuba to Florida, but otherwise what's the point?