I have searched all open sources and other electronic sources available to me, but not got any article exactly on "Reading habits of senior citizens". I think it's a good thing for your research, as no body yet touched this topic. I suggest you do your research on this topic and you may collect data from senior citizens regarding their reading habits directly. You should only refer the questions asked by other researchers on reading habits and also add your own questions in your questionnaire.
That what the true research is all about. Go head with your topic. Best of luck!