While 3/4 of my grandparents lived until their 90s, 5 generations isn't going to happen unless a couple of generations have kids in their teens.
We had plenty of 4 generation years, with my mom's parents. They died when my kids were 12 and 14. My kids saw them a lot and got a lot of history from them... some of it not exactly appropriate for kids. Did you know that Rose Kennedy liked to (insert Yiddish word here) the Jewish boys in the West End?
Still, it was a wonderful experience for my kids.