Heart rate is not similar in any manner to sinus rhythm/electrocardiogram. It is important, certainly, but not the same.
Safe that sorry is a diversion from the point/reason for the prescribing and or taking the medication; it is a preventative needed due to history of the patient.
What has age got to do with it? The result of AFIB is clear, and the danger is as well. Many people with AFIB find it to be silent, and go in and out from time to time. (I started with AFIB in 2017 discover in a pre op exam.
Originally I was on Plavix due to a TIA, but was switched to Eliquis when I developed AFIB. More bruising, but no clots or stokes; think of the hidden advantage, you get the drug ahead of time to break up clots, hmmm. Don't out think you doctor.
If your doctor says take it, take it or change doctors.
Good luck, and make wise decisions, I think you will.