Personally I do not believe in death or even ageing..
Compared to the vast continuum of infinite magnitude that is time, the life of any being, be it thousand years or a few seconds, is just too trifle..
Maybe some chemical rearrangement of the One who possesses infinite wisdom-- that is our lifespan..
The concept stands proved to my mind judged by the very fact that the living beings or organisms of varied species, as also being born in the same species, posses different levels of fitness and knowledge even at the moment they are born or are introduced to this arena by that Master..
The different levels could have in all probability, stemmed out of the prior existence of the being in some other form..Hindus believe in rebirth...
Hinduism in general would appear to subscribe to the idea of some inherited Karma, inherited intelligence etc, and also the Karma and intelligence or knowledge acquired during the lifetime..
Some believe that we are given each life to live off and compensate for the bad Karmas.. or alternately good Karmas practiced by us in earlier lives..
And it is something like a balancing of centripetal and centrifugal forces that is keeping the beings in the orbit of Karma, and it is also believed that the Supreme Being of Infinite wisdom can, if It pleases to do so, give us some small push, which can provide us escape velocity from this cycle..cycle of birth and death, and the orbit of Karma --unto emancipation, which we call Moksha..
He is never born in reality, nor He is dying, He had no origin,
He is eternal.. goes on Gita describing the Atma, and in advaitam the life force inside us is nothing but that atma..or paramatma..
Na jayate mriyate vaa kadaachit.naayam bhootwa bhavitaa na bhooyaH ajo nityaH saashvatoyam purano, na hanyate hanyamane shareerey..
Sannyasam is only a state of mind.. the four Ashramas of Brahmacharya, Grihasta, Vanaprastha and Sannyasa are deviced by the Lawmakers to give some orderliness to life.
In Mahabharatham Bheeshma's seven elder brothers were thrown away into river Ganga even as they were born to Her by Ganga herself, almost for this reason
Shankara could graduate to sannyasam at the age of seven, without entering the other ashrams..