This is a simple example of a choropleth map of grey pressure in 2016 in the Netherlands, with the (now) current municipality list of 2017. Grey pressure is the ratio between the number of people aged 65 or over and the number of people aged 20 to 65.
Find the official numbers on grey pressure in 2016 I used here. CBS.nl has all other demographic data on the Netherlands you might need, which can be easily reworked to fit this map. For a lookup table of municipality names and their 'gemeentecode', which you'll need for the join with the municipality GEOJSON, go here.