Aging begins the moment a person is born. A baby develops and matures into an adult. The stage where a decline in function happens that ultimately leads to death is generally called ageing.
Some changes during the ageing process are
Brain and Nervous System: As people age, the number of nerve cells in the brain decreases only slightly. Several things help compensate for this decline. Because of these changes, the brain may function slightly less well. Hence older people may react and do tasks somewhat more slowly. They also may show slow loss of vocabulary, short-term memory, the ability to learn new material, and the ability to recall words. After about age 60, the number of cells in the spinal cord begins to decrease. As a result, older people may notice a decrease in sensation. Therefore, older people are more vulnerable to injury and disorders.
As people age, the immune system becomes less effective. This slowdown may be one reason for occurrence of diseases like that cancer and infections, such as pneumonia and influenza.