Its difficult to find information about him. I think he is still with us although I am not sure. I don't know how old he is.
There is this web page:
http://www.kensmurals.com/Dave%20Christensen%20pinball%20line%20artist.htm
I don't know if that is still active or real. It says that you can contact this guy and he knows The Man.
After my first year or so getting into the hobby, I have learned a lot about him and I have 2 machines with his artwork, and have looked at many others. He is nothing short of an idol for me - his artwork is simply fantastic in my opinion. I just can't get enough of it and would have no problem making a pinball collection that just featured his work.
If he is still with us and even still has his skillz left - WHY DOESN'T SOMEONE GET WITH HIM AND COMMISSION HIM TO DO THE ART FOR A NEW MACHINE!?!?!?!?!
That would be EPIC