If you also wanna get pregnant, you should totally remember that the older you are the more difficult it becomes foe your baby to becom
If your periods have stopped, it indicates you have stopped ovulating. But age 51 is kind of on the edge for menopause. Sometimes women will go several months and then out of the blue will have ovulation, then a period.
If you are interested in no longer having to use birth control and not having a risk of getting pregnant, some of the women one reads about in Wikipedia who had babies later in their reproductive lives thought they were done with ovulation and periods, and then popped out an egg and got pregnant. So at 51 it is not foolish to still be cautious.
If you are asking because you are interested in getting pregnant, depending on how long your periods have been absent, it is still possible to get pregnant if you are willing to spend thirty thousand dollars or so for IVF with a donor egg and hormone treatments to create a lining in the uterus.