Greatnan they say that about prostate cancer and older men - because if you go looking a high proportion of men in their 70s and older would have some cancerous changes, often slow moving.
But because cancer is, predominantly, a disease of ageing cells, then an awful lot of us will, eventually, die of it. The thing about BC is that it is, in early stages, usually treatable - in fact curable - AND it occurs in an organ that we can manage without. And easy to get at for screening and treatment compared to prostate gland.
There is a good reason not to do mammograms in younger women (they don't work, because breast tissue is too dense) but not older ones (apart from the "too many x rays is not a good idea" argument.
Women should definitely carry on self examining into their 70s and beyond.