What the WTS/JWorg. did is create their own meaning and definition of what the word usage is toward Generation.
WIki and other sources have the usually accepted definition of the word Generation...
A generation is "all of the people born and living at about the same time, regarded collectively." It can also be described as, "the average period, generally considered to be about thirty years, during which children are born and grow up, become adults, and begin to have children.
The key point to their false acclamation is that once you past the typical life span of 100 years starting from 1914, the generation of people witnessing certain events of that generation(s) ends. A new generation has now followed the previous.
What that means is that the generation of people living now and for a few years more are not of the previous generation that witnessed events starting from 1914.