This is a really interesting theory and I agree with everything you said about taking care of your health.
I think that your theory could be very easily tested with simple survey methods. Find grandparents, ask their age, and ask if they regularly care for their grandchildren. It doesn't really matter the age of their own children because we can basically infer it with the grandchildren being under 12.
Such a survey could be improved by asking people their country. My anecdotal observation is that German grandparents provide much more childcare than their American counterparts, despite comparable generational gaps. Another anecdotal observation is the Filipino grandparents also provide more childcare with a smaller generational gap.
A fourth useful question might be to ask why grandparents are raising kids. I speculate that in rich countries, it is because they want to, but in poor countries, it is because the 20/30-somethings are financially providing for both the children and the grandparents.
I think that your theory could be very easily tested with simple survey methods. Find grandparents, ask their age, and ask if they regularly care for their grandchildren. It doesn't really matter the age of their own children because we can basically infer it with the grandchildren being under 12.
Such a survey could be improved by asking people their country. My anecdotal observation is that German grandparents provide much more childcare than their American counterparts, despite comparable generational gaps. Another anecdotal observation is the Filipino grandparents also provide more childcare with a smaller generational gap.
A fourth useful question might be to ask why grandparents are raising kids. I speculate that in rich countries, it is because they want to, but in poor countries, it is because the 20/30-somethings are financially providing for both the children and the grandparents.