Are people more likely to lose their faith in religion or become more involved in it as they get older?

The reason I ask this is because my grandmother told me that she once believed in God and was a regular church goer, when she was younger, but now that she's older, and with what she's seen throughout her life, she is a self proclaimed atheist. I've also noticed this with other elderly people I know. Do most people lose their faith in God as they age?