As humans, we are the most unpredictable creatures on the planet. We have such varying mental and emotional capacities, that as individuals, our actions are almost impossible to predict. But physically, we are much easier to figure out. We are conceived, we grow, we stop growing, and we eventually die. The framework of this process is completely beyond our control, but we do have quite a bit to say about the inputs and the outputs of each of these stages. Our actions play a part in how healthy we are during each phase and how long each phase may last (especially the period between early adulthood and middle age).
Further, the quality of the later stage (old age) depends highly on the quality of our most critical, middle age stage. If we can stay healthy and maintain a level of strength and fitness that resembles our earlier adult years, we can extend this stage and the transition into old age well beyond what most people believe is possible. But if we fail to maintain this level of health and fitness, the momentum of sedentarism will build to a point that will feel almost impossible to overcome.
