This is a math task. Given whatever you need (size of human population, probability of death at any age and similar statistical data) and assuming whatever you need (population distribution is such that it does not change over time or sth. like that) calculate average time between deaths of oldest individual in the world.
In other words instead of:
<google_search> therefore oldest man dies every 6 years.
I want:
<given_this_data_and_assumptions> -> <calculation_and_reasoning> -> oldest man dies every 6 years.
It depends on whether you want the oldest person as an individual or as a class. Good riddles shouldn't be forked.