How far the duration of human life can be extended is not known. The claims of hatha yogis are unauthenticated, while the theories of Christian Science and the experiment of Sri Aurobindo have still left it an uncertain matter. It is true that stories of centenarians being found in different parts of the world are not few and often pass unquestioned. But the difficulty of proving the date of birth usually remains. Most centenarians belong to the illiterate peasant class, to those who have not taken care to retain a correct knowledge of their age, for it was not so important to them as it is to the educated classes. There is hardly a record of payment by life insurance companies for the life of a centenarian. It is reasonable to ask, however, why, if the reparative and destructive elements in the body could be balanced, men should not live for centuries. In the absence of authenticated cases, we may only take the stand that Nature seems to have set her own limits to human life.
-- Notebooks Category 10: Healing of the Self > Chapter 1: The Laws of Nature > # 39