Explain the saying "old age is a state of mind"

Age is nothing but a number, according to new research that suggests you're only as old as you let yourself feel.

A study has shown that people who perceive themselves to be old and frail are more likely to give up activities which could help to keep them young – such as socialising and taking regular exercise.

By contrast, people with a positive attitude are more likely to continue taking part in these activities which helps them to stay fit and mentally alert.

the answer is c prevention of weight gain. i got the same question.