Woodcut images from 16th- and 17th-century books depict women in their three stages of life. The young, fertile girl is the first one. Still a virgin, she does not show the signs of bearing children and she is petite, with flowing golden hair. The second one is the voluptuous woman of child-bearing years. She shows the signs of having children on her body, and she is full and healthy. Then, thirdly and definitely last, we have the old hag or crone. She is no longer fertile, and her body is frail. The moral of the story is that the first girl will eventually become like the crone, and this is the cycle of life.
The same rule, of course, applies to men, no matter how often you work out at the gym. A young man dreaming of becoming one of the greatest piano players in the world should structure his plan for life with the three stages in mind. First he is young with a nimble will for learning, then he is wizened with a strong hand for performing. His twenties should be devoted to learning; his 30s, learning and practicing; his 40s, practicing and performing; his 50s, performing and teaching; his 60s, teaching and preparing the next generation.
Keep in mind that you will reach the third and last productive stage one day, and the fourth one is death, although this fourth stage may be more productive than all the others combined if your life plan is set up rightly. An old man who has reached greatness will soon reach decay, no matter how great he was, and in decay one should prepare for eternal prosperity.