These are the countries that have been democracies for the longest times according to weforum.org as of 7/3/2020 A.D. The link to my source is here: https://www.weforum.org/agenda/2019/08/countries-are-the-worlds-oldest-democracies
This is the age of the current form of government.
Not to be pedantic, but this feels more like a "years since the latest constitution" quiz. Also for some reason your source link redirects me to a list of countries by obesity rates