How long is a "Generation"?

I know people hate the word "Generational", but I suspect it's because we can't agree on how long a "generation" is. In the real world, a generation is 15-20 years, but that's a ridiculously long amount of time when it comes to the NFL.

To me, a generation in football is 5 years, the length of a rookie contract with the 5th round option. In that time, the league experiences 80% turnover, rookies become veterans, and veterans retire. So if a prospect is one of the best of the last 5 years at their position, to me, that's a "generational" prospect. Curious to hear what other people's thoughts are though!