How governments of richer countries have tried to cope with changes in population structure?

Most richer countries are experiencing fewer births and aging population. 
Some options richer countries have done to cope are:
- Investing more in the healthcare system, as more old people puts more strain on healthcare.
- Encouraging births so there will be enough young people to work and pay taxes in the future in order to support the again population who do not work. There are many ways of doing this, it has been done by increasing benefits and reducing taxes to families with children, giving them priority council housing / school and nursery places. France have even gone as far as to pay parents for every child, increase maternity leave massively and make sure women are still paid well when they are at home looking after little children. 
- Some rich countries that don't have enough workers due to decreased births have been allowing more migrants into the country to work and contribute to taxes.
- The age people can be before they can retire on a full pension can be increased (e.g. if you retire at 60 not 65 then you will get less money in pension).

The problem of malnutrition in bangladesh is caused in part by "over population."hope my answer has you : )