Longevity plays a big role. My grandmother is 96 and grandfather 94, so even with a first child at 29 they’ve still had over a decade with their great grands. I

Longevity plays a big role. My grandmother is 96 and grandfather 94, so even with a first child at 29 they’ve still had over a decade with their great grands. I had 6 great grandparents still alive when I was growing up. My parents were young, so will probably be in their 70s for great grand kids and if they make it near 100, could see great-greats (wild!).