Questions on DNA damage
Excellent question! 


You would definitely be able to find quite a few sequences of DNA that are undamaged (in fact most of them would be undamaged), but it is very unlikely that any cells in his/her body would have a perfect copy of the entire original genome.
I'm sure that cells closer to the skin (exposed to more radiation) would have more mutations, but beyond that most everything depends on where you live, your habits, etc. (if you're a smoker you will obviously have more mutations in your lung cells).
Under regular circumstances (low levels of mutagens), about 3 nucleotide mutations occur in the human genome per cell per division (DNA replication) (from http://www.ncbi.nlm.nih.gov/books/NBK26881/). The rest of the math would be a very rough estimate, seeing as you'd need to make a lot of assumptions (cell division rate average, other mutagens an organism may encounter, life span, the list goes on), but however you want to do it, there's the number you need to start with.


I hope this helps.

CDB