I think you need to specify what you mean by "longest running democracy". Because democracy isn't like instant coffee, as in just pour in a hot water cup and it's there. It often was a long process, often changed and still being changed today.

For example, is a democratic system that excludes women or other groups from voting still a 'real' democracy as we perceive that term today? What are the minimum requirements for a country to be considered "democratic" ?