Why Cancer Rate Increases With Age

James DeGregori's  hypothesis is that cancer is not the result of the accumulation of DNA damage, rather changes in tissues due to aging, which make the tissues more susceptible to cancer.  But he doesn't explain how.  Just because cancer doesn't exactly follow DNA mutation frequency (mostly in young adults) doesn't mean that cancer isn't a result of DNA mutations.  One could say based on his hypothesis that children shouldn't get cancer, yet they do.  He needs a better mechanistic explanation.