You lost because the definition of a generation does not cover a specific period of time but in fact covers the people born at around the same time. Therefore it's actually a reference to population and not to time; a generation is a group of people and not a time period. Strictly speaking a generation can be defined as all those people born on 26th February 2021 if you really wanted it to. Common perception is that around 20 years is a generation but that's just not factually accurate.
I can't understand why you can't get your head around that - maybe it's a generational thing?