I am 51 years old, and my period is 16 days late. how likely is it that i am pregnant? or is there something else that could be causing this?

Low risk - pregnancy: At age 51 the chances of being pregnant are quite low (but you can still take a pregnancy test to find out). If your periods have been regular up until now - you might be perimenopausal. For on-going irregularity - d/w your gynecologist. Take care.

Perimenopause: The average age of menopause in the United States is 55. At 51, your fertility rate would be expected to be very low, but if you are still having periods, you could still get pregnant. The absence of a period for a year if the longstanding definition of menopause. The years leading up to menopause are called perimenopause. Periods can become irregular during perimenopause.