ElderBerry, JW Facts has a good page on the generation teaching and how it changed in 1995.
https://www.jwfacts.com/watchtower/generation.php
Before 1995, the idea was that the generation that saw the events of 1914 would not pass before the end. By 1995, that generation was in its 80s and 90s. They practically dropped the teaching, only to revive it in a modified form in 2010 (the overlapping generations teaching), which I think has been a huge mistake for them.