Why not a hundred years really isn't that long a time, my grandfather will be a hundred in only two years. If you think about it Tsunade's grandfather was the first hokage and she is already in her mid 50's so the village could easily be over a hundred years old.

I would consider a generation to be about 25-50 years and if the first and the second were from the same generation then there is still the third's, the sannin's, the fourth's, the ninja's kakashi's age and up and finally Naruto's generation. At a minimum that is atleast 150 years.