I'm 37 and haven't done very well with this!
All of my grandparents were gone by the time I was 22, and 2 of them while I was still a child (9 and 11 I think).
My dad went very unexpectedly when he was 62 and I was 32.
My mum is still going really well and is 67. But her parents were both dead by 75, so I'm very aware that we might not have aaaaages left together.
Saying that though, all great grandparents lived WELL into their 80s and 90s, so maybe there's some hope there!