A person's average body mass index (bmi) is the lowest between the ages of:

Between the ages of 5 years to 6 years old

This is an esteem gotten from the mass (weight) and stature of a person. The BMI is characterized as the weight partitioned by the square of the body stature, and is generally communicated in units of kg/m2, coming about because of mass in kilograms and tallness in meters. It's usually lowest for kids between 5-6 years old