Old people give up their mobility way too fast, often because of depression, isolation, or sheer lack of anything to do. A device like this will only accelerate the process. Young or old, we all tend to perceive a certain level of exertion as unpleasant, even dangerous, and that level is well below the level of exertion required to keep us fit and healthy. Obviously we are very poorly adapted to living in an environment where physical exertion is optional. The more we make exertion optional, the faster our bodies will degenerate.