A 2010 study revealed that a decrease in T explained much of the loss in phase III and IV sleep, or "deep sleep" that is characteristic of aging males.  At age 50, men spend 5-7 percent of their sleep time in Phase III and IV and by age 60 it is nearly zero or nonexistent. Young men, on the other hand, spend 10-20 percent of thier total sleep time in these stages due to neuronal integrity and abundant testosterone levels..
The key to masculinity and vitality is the human growth hormone that separates the boys from the men. It plays a vital role in the creation of muscle mass and strong bones. It contributes to deep voice and even sex drive. Low testosterone in men is known as hypogonadism. As a product of a modern world made for convenience the male body does not go through nearly as much rigorous activity. The lack of daily exercise contributes to the decrease in male testosterone. It can hit as early as the mid 20s and steadily decrease each subsequent year.