Much like the practice of calorie restriction, exercise changes everything for the better in most people - it is far more effective in improving and sustaining long term health for the majority of us than any presently available medical technology. We need the future of better medicines that will achieve what good living cannot, such as rejuvenation of the elderly, absolute prevention of age-related disease, and radical life extension, but in the meanwhile it makes sense to make the most of present and proven methodologies to better out position as much as possible. People in the middle of life today will be cutting it fine under the most optimistic estimates for the development of working rejuvenation biotechnology - every year counts when it comes to either making future technology arrive more rapidly or being able to wait for longer.
The present phase of rapid development in biotechnology is uncovering a great deal of new knowledge when it comes to the workings of exercise: how exactly, down to the level of cells and signals, it improves health and life expectancy. For example, here is a paper on exercise and the brain:
The benefits of exercise and physical fitness on mental health and cognitive performance are well documented ... Animal studies have also demonstrated that exercise or physical activity produces very specific changes in the brain that are distinct from those produced by learning or novel experiences. ... Recently, studies have been carried out in humans using non-invasive brain imaging techniques to investigate exercise-related changes in brain structure. Such studies provide compelling evidence for the powerful effects of exercise on the brain, but also raise several questions. For example, do structural changes occur throughout the brain or are they limited to specific brain regions? What aspects of brain architecture are specifically modified by physical activity? On what time scale do these changes occur, and how persistent are they when exercise is discontinued? Do specific preconditions such as aging, disease, or genetic phenotypes make individuals more or less susceptible to activity-based brain changes?
Although relatively few studies exist on the effects of aerobic activity on the brain structure of healthy, younger individuals, there is a wealth of data demonstrating the cognitive benefits of frequent aerobic exercise throughout the lifespan - perhaps none more convincing than a recent study of 1.2 million Swedish military conscripts that showed a strong correlation between fitness and intelligence. Much work remains to be done to determine what level of aerobic activity is required for cognitive and brain health to be maximized, but it seems likely this level is well above that of the average individual.
You might compare that conclusion with data on life expectancy in athletes:
- Atheletes Live Longer, Probably the Exercise
- Putting Upper Bounds on Longevity Derived From Exercise
But equally, it seems clear that even moderate regular exercise has great benefits - the 80/20 point is probably somewhere in the vicinity of the venerable recommendation of 30 minutes of some aerobic activity. Sadly, even that level of exercise is probably "well above that of the average individual" in the wealthier nations.