The most widely accepted factor is Africa’s youthful population. Only about 3 per cent of Africans are over the age of 65, the age group in which illness and death from the coronavirus are most common. (By comparison, about 18 per cent of Canada’s population is over the age of 65.)
Africa’s low COVID-19 death rate has multiple causes, WHO says — https://www.theglobeandmail.com/world/article-africas-low-covid-19-death-rate-has-multiple-causes-who-says/
- Case fatality rate of 2.4
- lower testing rates
- youthful population
- 90% of cases in people <65 years of age
- more rural areas, more time outdoors
- strict lock downs early
- poor road network, limited international flights
lifeunderwriter.net 
Why is Africa so youthful? Because the Life expectancy is low?
It would be interesting to look at the fatality rate in some of the blue zones where there are multiple centenarians living. Sardinia and Okinawa and Lima Linda come to mind.
People don’t live long in Africa so life expectancy is indeed low. If you are referring to the Covid-19 fatality in the blue zones that would be very interesting especially the Loma Linda population due to their diet and avoidance of alcohol.