Simply enjoy the walk. Notice the richness of your surroundings. Let your senses drink in the beauty of nature and the crispness of the air for a change. So many people who have mastered the art of growing younger have also mastered the habit of a daily walk. Start a program of weight lifting at the gym.
Strong people are mentally tough people.
As you age, you need not lose your physical nor your mental strength. Whether you are 19 or 93, stay fit, stay motivated and stay passionate about life. Remember that effective time management makes you more rather than less flexible. It allows you to do the things that you really want to do rather than the things you really have to do. Do not take personal development books as gospel.