[Advaita-l] prana and the lifetime

[Michael Shepherd]

Friends,

For reasons individual and universal, I'm interested in vanaprashtha -- and
so will others need to be, if as recently estimated, babies born now will
live a hundred years..

I read yesterday that prana is directed, up to the age of forty, to the
activities of the physical body; from forty to seventy, to mental
development; and from seventy onward, to spiritual development.

Is there any scriptural authority for this statement ? In Ayurveda perhaps ?
In Saivism ? It seems open both to interpretation and misinterpretation as
it stands.

Michael