Aging is of two types; one is biological aging and other is mental aging. Biological aging is chronological. Every tissue of our body is having a fixed life span and it is decided at the time of its formation. With the passage of time, its capacity to do work keeps on decreasing. That's why with age, our eye sight is affected, kidneys may create some problem, greying of our hair occur, joint pain my happen and so more like this. This is unavoidable.
Mental aging is that, we may be young otherwise but our thinking is pessimistic. We always begin something with 'NO' or 'I can't'. We don't believe in our self. We always try to find out the excuses for our failures and blame others. There is no specified reason for it. But it is the APPROACH that makes a person mentally aged.