There's some benefit to exercising at 180 - your age beats per minute. This will be fairly low.
You could also alternate jogging and walking to keep the heart going in range.
You could seek out some hills for your walk. Even overpasses are hills, although not as pleasant as quieter streets. Stadium steps are another option.
You could just walk at a purposeful pace and enjoy the outdoors and not care about your heart rate. I honestly believe that walking at a human pace out in the sun, out in nature, is one of the healthiest things you can do for your mind and body.
Female, 5'3", 49, Starting weight: 163lbs. Current weight: 135 (more or less).
Starting squat: 45lbs. Highest squat: 167.5 x 2. Current Deadlift: 190 x 3