Check your target heart rate zone by age before runs
Added
Estimate your maximum heart rate as about 220 minus your age, then aim for roughly 50-70% of it on easy or moderate days and 70-85% on vigorous ones. Use a watch or count your wrist pulse for 30 seconds and double it. Some medications lower heart rate, so ask your doctor what your zones should be.
The result
Result: American Heart Association: the age-60 target zone is about 80-136 bpm with an age-predicted maximum of 160 bpm (age 65: 78-132 bpm, max 155); the figures are averages to use as a general guide.
Note: Not medical advice. Talk to your doctor before changing your training, diet, or supplements.
Source
American Heart Association: Target Heart Rates Chart (opens the original source in a new tab). Check it for the latest numbers before you act.