Yes, grandparents have raised their own family but human instinct is to love and care for children and grandchildren forever ,regardless of age
Well, that must mean that my wonderful, generous, loving but now aging parents are sub-human because although they love all their children and grandchildren dearly, they certainly don't care for them. They care a lot ABOUT them, but they've done their time and now they're resting, prioritizing their health, and enjoying themselves. Which we siblings are very happy to see.
I have no intention of giving up more of what I want from my life to rear or help rear my grandchildren. I have given up almost everything for my children, willingly and happily: for what will probably be more than 2 decades (and as I'm a woman, probably the healthiest and most valuable decades of my life) I am giving them the absolute best of myself so that they can go on to be fulfilled, independent, secure, confident and capable adults. It's entirely up to them what they do with their lives - children or no children, career or no career, whatever. And, once I'm confident they're able to stand on their own two feet, I will go back to making my own life a priority, be it through studying, traveling, voluntary work, focusing on neglected friendships, hobbies. I'm sure I will love any grandchildren dearly, but no, I won't go back to tending and providing. If I have grandchildren, I would like a similar sort of relationship with them that my parents have with my children: full of fun, enjoyment, interest but absolutely none of the drudgery.
Isn't that the way of life? Children are but one part of a full life. They're not an entire reason for being.