Is 53 beats per minute too low for a human heart for a 45 yr old?

Yes, that is normal. Here is a general standard of pulse rate (PR).

Resting Pulse Rate

PR < 40 BMP - Below healthy resting heart rates.

PR 40-60 BPM - Resting heart rate for sleeping.

PR 60-100 BPM - Healthy adult resting heart rate.

PR 100 BPM - 220 BPM - Acceptable if measured during exercise. Not acceptable if resting heart rate.

PR > 220 BPM - Abnormally high heart rate.