Multiple choice The average twelve-year-old child has a mental age equal to 100 120 10 12 Reveal answer Fill a bubble to check yourself D Correct answer Explanation Mental age represents the age level at which a person performs intellectually. By definition, the average child's mental age equals their chronological age. An average 12-year-old has mental age 12, just as an average 10-year-old has mental age 10.