Age 40 . Most reputable medical institutions recommend beginning yearly screening at age 40 and continuing until no longer physically able.
You are 42, so you should begin annual screening now.
For most at 40. The U.S. Department of health and human services, american cancer society, american medical association and the american college of radiology recommend screening mammography every year for women, beginning at age 40. Those with a family history of a 1st degree relative (like your mother or sister) having been diagnosed premenopausally with breast cancer start 10 years before the age of diagnosis.
Age 40. It is well-established that mammograms will find breast cancers well before most people would ever palpate it, and, in defined age groups, saves lives. Controversy exists whether to start screening at age 50 or 40; in the US, most doctors recommend yearly mammograms at 40. It is also controversial whether to get mammograms after age 75;; this is more dependent on a woman's physiologic age.