Since  a few people have been searching for “how to draw an old man” let me expand. Sorry this is words and not images.

1. This was a quick sketch that  drew heavily off of inspiration and stock photos. The inspiration was American Movie, and Uncle Bill captured my heart. In no way is this drawing a representation of him but it kick started my brain into old-man mode. Just a quiet, contemplative, death-and-meds kind of introspection, followed, of course, by incoherent rambling (which I will excel at as an old man). The important part is that there is a feeling behind it. Try to think about why you want to draw what you are drawing. The mentors tell me art is based on feelings, anyway.

2. Drawing old men is amazing because wrinkles brings you into a landscape-type scenario and landscapes are a special kind of controlled chaos. You can experiment with the mark making you want as long as it follows the basic sort of skull shape that makes a human face.

3. Learn how to draw a skull / take a life drawing class / draw from observation a lot. Nothing beats cold hard repetition.

4. That being said, some of these references help me out in a life-drawing pinch.
http://www.posemaniacs.com/ < Good for different angles and stances. The body moves around easily.
http://www.nationalgeographic.com/ < Faces of all sorts grace the pages of this publication. This was probably my first source of reference for copying the human face.
Look into proportions of the human skull and human anatomy. Generic is better than no basis of reference.

5. My favorite tip: Flip your drawing a quarter of the way through, either in a mirror or Photoshop. You really get a sense of whether or not a certain angle or shape is laid in correctly.