Final answer:
Donald is most likely to be 5 to 6 years old if his BMI is currently at the lowest point it will be for his whole life, as this age typically precedes the pubertal growth spurt.
Step-by-step explanation:
The student's question refers to the point in a person's life when their Body Mass Index (BMI) is likely to be at its lowest. Considering growth patterns in children and adolescents, Donald's BMI would most likely be the lowest during his pre-pubertal stage. During middle childhood, which is typically from ages 5 to 6, children typically experience a leveling out or lowering of BMI before it increases again during puberty.
To answer the student's question, Donald is most likely 5 to 6 years old if he is at the lowest BMI he will have in his life, as this is a common age for the BMI dip that precedes the pubertal growth spurt and potential increase in BMI due to increased body fat and muscle mass.