I didn't say the poor countries didn't have lockdowns. And a delayed impact was expected, because of the lack of travel to those countries. A greater impact could still happen there, but so far there's this mysterious lower death count in the developing world, as the article I cite shows.
The virus has been confirmed in the poorer parts of Africa and in other developing areas, so the question is why the death count isn't higher there rather than lower, given the lack of medical facilities. Fareed Zakaria was expecting a massive wave of deaths in the poorer countries when the virus finally hit them, but there was no such wave.
You suggest the people there don't make it to old age, on average, so if the virus mainly kills off old people, that would explain the lack of impact. That might indeed be a factor. But it could also be offset by greater underlying medical conditions in the poorer populations, due to poverty, which would exacerbate the virus's impact. According to the article, it's a complicated problem.