6.16. The decline in fertility levels, reinforced by continued declines in mortality levels, is producing fundamental changes in the age structure of the population of most societies, most notably record increases in the proportion and number of elderly persons, including a growing number of very elderly persons. In the more developed regions, approximately one person in every six is at least 60 years old, and this proportion will be close to one person in every four by the year 2025. The situation of developing countries that have experienced very rapid declines in their levels of fertility deserves particular attention. In most societies, women, because they live longer than men, constitute the majority of the elderly population and in many countries, elderly poor women are especially vulnerable. The steady increase of older age groups in national populations, both in absolute numbers and in relation to the working-age population, has significant implications for a majority of countries, particularly with regard to the future viability of existing formal and informal modalities for assistance to elderly people. The economic and social impact of this "ageing of populations" is both an opportunity and a challenge to all societies. Many countries are currently re-examining their policies in the light of the principle that elderly people constitute a valuable and important component of a society's human resources. They are also seeking to identify how best to assist elderly people with long-term support needs.