Because all children want to have active young parents and active grand parents as long as possible.I remember one my girlfriend,who was born when her parents were 40(now they died both)and she told me even before,that it`s gave her a lot of bitterness,that she always felt sorry,that her father died when she was child,and she never saw her parents young.That`s lack of support and psycological trauma.And compare to people,who normally can know not only grand parents,but even great-grandparents,as we used here.