A bloody discharge that is confirmed by your doctor to have been caused by cervical erosion does not render you niddah.
In general, even if a woman is diagnosed with cervical erosion, she should still be concerned about the bleeding around the time she expects her period. Since you are over the age of 53 and do not have regular periods anymore, you need not be concerned by this discharge.
Due to the sensitivity of the cervix, it is common to experience bleeding after intercourse. While even this bleeding may be attributed to your condition and disregarded, we still advise that you avoid looking for blood after intercourse.
You should also speak to your doctor about treatment options which sometimes are effective in reducing the bleeding.
Please feel free to get back to us with any further questions.