Debra Whitman at the Wall Street Journal: Stress about growing older becomes self-fulfilling. The stress itself causes physiological health problems.

Also:

… our expectations about growing older become self-fulfilling because they affect how we behave. For example, while a positive attitude about aging doesn’t take the place of exercise and eating well, a belief that we can live long and healthy lives often encourages people to invest in their future selves by taking more walks and eating more greens.

On the flip side, when we view health problems as inevitable, we’re more likely to see healthy behaviors as futile. [And:] When older people believe that unhappiness comes with age, they are less likely to seek treatment for depression.