I had talk about the generation overalap with my siblings in the 1990's around the time I walked away. They had insisted that generation can span in multiple biogeneis, as long the belong to the same political system. They explained that Renaissance lasted 200 years and anyone alive between 1400's and 1600's were part of the same generation, the Renaissance generation. The same the believe that people alive today who knew people born before 1914 and will meet in the future younger generations born in 21st century are still a part of the same generation, the last one. So, in theory, the 1914 generation can be alive as well until 2214. My grandparents were born around 1900, and died in my teen years and my nieces and nephews born at the turn of the millenium and living for another 80 years are still part of the same generation.
Either way, the concept of the last generation is a problem for Christianity. Since the 1st century there was a debate what represent the last generation. I am sure the Apostles were not expecting to age and die and were hoping for promised Jesus return. Every generation of Christians since that time believed that they are the last one.
I heard the discussion on TV while ago why are Christians so preoccupied with the End of the Day and the asnwer was that they want to know how much time they have left on this earth so they can fully enjoy it with all these earthly pleasures.