It has been said that those born prior to 1956 might have some immunity. This may have some basis in fact, but as I read info from many countries recently, I am seeing more older folks dying now. It may be that they have more prior existing health conditions that may make them more susceptible to infections in general.
Also, as the virus makes its way around the globe in successive waves, it mght tend to target different populations with each pass.
This would be consistent with the history of past pandemic influenzas.
We will know more as we go along. It is still relatively early in the pandemic which we can expect to last for over a year...