Drawing and painting faces is the most difficult thing there is. I have learned this over many years, as well as hands and feet, and the key is in the folds or wrinkles, as you mention. In all cases, this is achieved through a combination of light and shadow to create a sense of relief, of actual volume.
But your practice has put you on the right track. You've drawn a very good portrait, and the best way to keep improving your work is to keep drawing. Very, very good work!
I have picked this post on behalf of the @OurPick project! Check out our Reading Suggestions posts!
Please consider voting for our Liotes HIVE Witness. Thank you!
RE: Graphite portraiture of an old man