As noted in the New York Times, the beneficial effects of low-calorie diets are available at any age (in flies at least). This follows up on similar research in mice that shows calorie restriction brings on beneficial changes in genetic expression very rapidly. It doesn't matter at what age the diet is started. You do have to stay on the diet to maintain the beneficial effects, however. What are you waiting for? Try calorie restriction today! You'll feel better and live a longer, healthier life.