Sir82 clarified things but I would add that the WTS made two representations of generations into one on their own, people born around 1914 and people born from out of that generation or two life spans conjoined as it were.
That's not what Jesus said as in " This Generation " as a singular description.
This description would therefore include new borns and the old, a generation in biblical chronology time is a complete life span 80, 90 or perhaps even 100 years.
Another way of looking at from a WTS perspective , lets say a person had a child in their 40 's or 50's who were themselves born after 1914, then their offspring would be included in " This Generation " .
But that's not what the WTS once said for very long time .
Interesting enough in that that is the actual age group who are now presently the GB members of the WTS/Jworg.
So from using the year 1914 as a start date we can see that things would have to occur no more than 100 years from 1914 as a Biblical generation , that's if you were to adhere to Jesus's description of " This Generation "