You know what, I actually changed my mind. Not because of you, but because I googled the issue. And as usual I was right, correlation/causation and other silly things:
http://www.huffingtonpost.com/2012/04/15/religion-health-well-being_n_1423713.html
"It’s also true, researchers say, that people who regularly attend religious services enjoy a boost in their happiness. However,
research findings don’t agree on how much of the benefit is religious and how much derives from the benefits of social networking and being with other like-minded people.
It just puts people in touch with like-minded congregants,” he says, and thus produces many of the benefits of a strong social network. “It’s a period of time when you can actually connect with others and you’re not alone in your beliefs.”
To identify a deity “bonus,” though, is much harder. “You have to break it down into components and look at religious activities and religious beliefs,” he explains, “and you have to look at them during times of stress. Is it the activity? If so, which kind of activity? Is it the belief? If so, is it [a belief in] life after death” or some other belief?"
In plain English, per se it is not the being a believer that helps with longevity, but certain dietary restrictions, leading a moderate lifestyle and being among friends and people with similar beliefs.
TL;DR: You don't have to be a Mormon to live long, as long as you don't smoke, moderately consume alcohol and caffein and you are a member of a chessclub or singing choir. And eat Australian beef! 
