According to William McCoy for the Houston Chronicle, the average heart rate varies based on a person's age. An average 50-year-old woman who walks a mile at a brisk pace has a heart rate of 85 to 119 beats per minute.
McCoy says that an average person who walks a mile at approximately three miles per hour (around 20 minutes per mile) has a moderate heart rate. A moderate heart rate is defined as 50 to 70 percent of the maximal heart capacity, which depends on the age of the person. A crude estimate of the maximal heart capacity can be obtained by subtracting the age of the person from 220.