I think genes do play a part in longevity. In the past what killed people was infectious disease. Clean water, an understanding of the transmission of infection and effective treatments did much to increase longevity, it meant far fewer children died before they rerached five and if you remove the deaths of vast numbers of under 5s from the calculations average life expectancy soars.
I come from a family that has been long-lived, over four or five generations, my great great grandfather died in his late 80s despite being an Irish immigrant living most of his life in poverty in Victorian London slums, my great grandmother born and living in similar circumstances lived to 82. My father, one of 11, lived to 92 qnd so far that set of siblings has had 2 nonagerians, another one hitting 90 this year and another two younger ones heading that way. Average age at death has been over 85 and all, bar two, have been mentally and physically fit and healthy until within months of their deaths. Their children now beginning to populate their 70s have a history of good physical and mental health and none are showing any signs of decline into poor health, one died in a road accident, one has had cancer and recovered, but that is all.