Or maybe those who look younger haven't needed the protection of aging because they've accumulated much less DNA damage in their lifetime (because of low sugar diet, slow basal metabolic rate, etc.), and less DNA damage = lower incidence of cancer.

Asian Pacific Islanders (API) (who appear younger than they are in general, in my opinion) have the lowest incidence rates of cancer out of all races (for adults).

http://seer.cancer.gov/report_to_nation/

My understanding is that we all have cancer cells in our body — the problem becomes when they get triggered. There may be something in the immune system that has something to do with this. What depresses me with this subject is that it seems like the more we know about it the more we understand how much more we really need to learn. Also as I get older I keep coming across more members of my peer group (and people I know who are older) who get some form of cancer. It seems like we've made some progress in my lifetime, but it's too slow for my tastes. In my dream of dreams someone would come up with a silver bullet.