Possibilities thrown out about cessation of fertility for men and
women.
Childbirth becomes more dangerous as the age of the female increases.
Pregnancy is an extremely complex and energy intensive process that
greatly taxes the childbearer.
Perhaps grandmothers are useful to have around in early human societies.
Men do not expend much energy in the mechanics of being fertile and
having children. There does not seem to be any disadvantage to keeping
the machinery going until death.
A point to be made about lifespan. As far as is known, the maximum lifespan
has not changed much if at all in the last few thousand years. The
ability to attain the maximum lifespan for a greater number of people has
increased significantly.
