"Population ageing - the growth in the proportion of persons aged over 60 - represents one of the most significant demographic processes shaping the world today. The trend is an inevitable product of the shift from traditional to more modern forms of demographic reproduction. Because of historical, political and cultural differences, and depending on where countries may be on the continuum of demographic development, the issues arising from population ageing take a variety of forms." (Quoted from paper) (The paper is only available through the link)