The impact of grandparents being older? Well, it seems to be a double-edged sword.
Our first grandchild arrived when we were 60-years-old (two more have since followed). My parents were 46 when their first arrived.
The benefit in our case was that my wife had just retired and I took early retirement one year later, therefore, we were available for regular child minding duties. The negative element is that in our sixties, healthy though we are, trying to cope with lively and demanding children can be (is) very draining.
For my parents those two factors worked the other way round.
Perhaps in the 1960s & '70s the old-established family pattern of a working father, a housewife and 2.4 children was still in evidence, but now the nation's economic situation has changed at the same time as its demographic situation, i.e. mums need to work to get enough family income to survive and the older generation are living longer so as to provide the child care, thereby allowing the mums to work.
It seems we have no choice but to join in with the new status quo.
Will the availablity of a longer-living older generation be a factor in a couple's decision to have children - or not? We need, as a nation, to provide proper financial support to young parents so that the pressure to have children later in life is eased. At the moment couples feel the need to have established their financial security and their housing requirements before having children. This makes for "older mums" and "older grandparents". We would be better off if we could reverse that trend, not just for the sake of the grandparents but also for the parents who at, say, 55 will be battling with teenage off-spring.