via Discovery News:
...increased life expectancy results in a "postponement of religious involvement," especially for religions that don't tie eternal rewards to time and favor ideas such as personal salvation over predestination.
This may account for an increasing number of churches, synagogues, mosques and temples seeing "greying" religious congregations, researchers say.
Although other factors influence religious participation, age alters how people perceive the costs and benefits of religiosity through time. People may consider the time and effort taken to worship as a cost, while weighing the benefits of gaining a sense of community, greater spirituality and personal confidence in the afterlife.
In places with low life expectancies, the risk of dying is more of a reality, which may account for higher religiosity, the researchers say.