Why do people age and die ?

Here is again an explanation found in 'the selfish gene' regarding the phenomenon of aging and death.

Aging is attributed to a lethal gene which gets activated only after a certain point of time. Why has this gene survived ? simply because this gene does not come in the way of reproduction and such stuff. If this gene had got activated much before, say at the age of 11, then, probably it would not have survived.

Why isn't there an allele(competing gene - which has some other effect than aging) for this gene ? May me at some point of time because of mutation and such stuff it may get created. Or may be it was there before and people used to live for ages and it got extinct because of natural selection - it wasn't favorable! As to why it is, requires another session of thinking.