About 16% of Japan's 126 million people are now over 65. By 2015, the figure could be one in four. The reason for this is improving health care, allowing people to live longer, coupled with a declining birth rate. The Japanese have the highest life expectancy in the world. At the same time the fertility rate is now 1.39, well below the replacement level.If things go this way, Japan's population will have plunged by half by the end of the next century.