What does a 25bpm indicate in an 89 year old women?

That's obviously abnormal. Commonly such a rate is due to heart block where the messages for the heart to contract do not reach the ventricles, but sometimes it's sinus node (the native "pacemaker" in a person's heart) dysfunction. In either case, unless the underlying cause can be reversed, a pacemaker would be indicated.

Also the rate could be due to an erroneous measurement, especially when it's obtained by checking the pulse. With bigeminy, for example, where every other heart beat is a premature ventricular contraction, often only every other heart beat is felt in the pulse (so the real HR is twice what is measured).