The Causes of Premature Aging And Geriatric Disease Birth, growth, old age, and death are the natural order which no life can resist. Without birth there can be no death and vice versa . Life and death together form a circle which rolls on forever. Human beings are not outside this natural condition.
All animals have their own life cycle of growth and decline.
When 20 years old, qi and blood become strong, the muscles are firm, and so one becomes good at fast walking. When 30 years old, the five zang are all solidly built and the muscles are strongly formed. One's blood vessels are full so on is good at running. When 40 years old, the five zang and six fu along with the twelve channels are over their peak and are starting to decline. The hair starts to turn grey and one is good at sitting.