The tissues, as age advances, become more rigid and less elastic, the bones more brittle, the ligaments stiffer; deposition of fat in internal organs (for example, the heart) weakens their activity; the skin becomes thin so that cold is more acutely felt; the walls of the blood vessels become at first thicker, then more brittle, so that haemorrhage more readily occurs. There is poorer blood supply to the brain, hence mental feebleness. Teeth and eyes weaken. Because people do not age at the same rate, a given individual may appear, physically or mentally, either younger or older than his true chronological age.
30% of the characteristics of ageing are due to one's genes, the remaining 70% are not. Successful ageing is aided by regular physical activity, continued social connections, resiliency to setbacks, and a feeling of control over one's life.
Within the next 45 years the total number of elderly in the world is expected to reach over 1.1 billion, with 75% of them residing in developing countries. By the year 2025, Asia will account for approximately 57% of the world's elderly, Africa and Latin America for about 20%, and the developed regions of Europe, North America and the USSR for approximately 25%.
A US survey of adults revealed that 63% would prefer not to live to 100. The leading reason for their reluctance is a fear of being in poor health; a second reason, cited by 38% of the poll, is the fear of not having enough money.
The process of aging is not a disease. The Baltimore Longitudinal Study of Aging, a long-running inquiry into aging and one of the most comprehensive in the world, has noted that personality does not change with age, most mental capacities remain constant, and healthy organs continue to function.