The Clock of time goes on and on winding  itself in the womb of past with every tick it makes, never to rewind, never to come back. The moment gone is gone forever, contemplating on life, it is like the ticks of an internal clock wound to zero at birth, to the end of life span of an individual which varies from one life to another. Life span is the maximum time that a person could live under favourable living conditions. It is the boundary of life that one lives which is unpredictable and unchangeable. But the idea or notion of longevity can be much in contrast with the idea of life span.

Life span can be much shorter duration or very much of longer and flexible time period of decades and decades. The golden splendor bettle has a life span stretching for more than four decades. In California there exists sequoia pines that started growing when the Egyptians were first building their pyramids. Contrary to this fact of killifish in Central Africa lives only eight days. There are insects that are born in the morning, are sexually mature in the afternoon and are dead by the night fall. Even a baby in the mother’s womb dies after it has had life inside or even sometimes immediately after birth or may be a few minutes, a few hours, a few months, dies after that life span, which is the ultimate boundary line for each individual. But again the characteristics of this life span are flexible taking into consideration the life style, and circumstances under which the human life develops under favourable living conditions. The process is flexible enough so that you can do the reverse to a limited extent. Sterilize a dog, male or female, and you will extend its life by two years. A human who stops smoking increases his or her life by many years. Even through the performance of trained training of yoga, concentrating on the breaths that we breathe,  Converging all the faculties to the eye centre, increases the life span for sure, for it is a believable fact that we live in breaths, not in years. For every organ, every tissue, every cell of the living being has its own time period to age and the same reversible fact can be applied to each and every organ by the provision of exercises, proteins, stimulants and the necessary requirements they need; but not to forget that all goes well along for a  a limited extent. The span remains the same, longevity varies.
       
No evidences exist that the maximum increase in one’s life span in increase by  regular physical activity.  People who have increased physical activity only add to a better positive attitude in life, it definitely improves the quality of life in later adulthood. But any proof of stretching the life span is not found; not it is logically acceptable. An elderly person in the best shape, who has maintained his life by regular exercise and diet, is not as strong as a young man who doesn’t know much of ABC of exercise, nor is the elderly man as capable as the young in performing tough tasks which require muscle power. The fact remains that aging also ages the bones, the muscles and the joints besides skin and hair. Any kind of precaution as yoga or exercise or aerobics whatever may be, can never succeed to halt the tickling of the clock of ages.
          
Youthful English poet John Keats, before his literary writings , was a physician but when in love with a young and wealthy woman -Fanny Brawne was inspired by her towards poetry writing. Later suffering from acute TB, coughing blood every couple of hours, he felt the touch of death so immortal. In the end he surrendered his totality to its power, its inevitability and its ability to relieve gently his chronic suffering. In one of his writings we read the following:

Verse, fame and beauty are intense indeed
But  death intenser, death in life’s need
My spirit is too weak-morality
Weighs heavily on me like unwilling sleep
And each imagin’d pinnacle and steep
Of God like hardship, tells me I must die!