The world is about to experience a demographic revolution. Throughout history, the elderly population (people aged 65 and over) never amounted to more than 2−3% in any country. Today, in developed countries, the elderly population ac- counts for 15% of the total population. The United Nations projected that by 2030 the elderly population will increase to 25% and nearly 30% by 2050. Soon, the elderly population will out- number children under age 5 for the first time in human history.