Here is a general guide to drawing elderly people's faces and figures. A general age progression chart is provided below, and example illustrations for you to reference. Wrinkles are obviously added to the face, but other things change as well.
This is one of those things that they really didn't teach me in art school...how to show age progression of a face. Here is some how-to tips for drawing old people's faces and hands. I hope that it helps you.