Gynaecology & Obstetrics General ac3e3574 Gonadotropin levels decline to prepubertal levels by age A 6 month to 1 year of age B 1 year to 2 years of age C 2 years to 3 years of age D 3 years to 4 years of age. High-Yield Explanation Gonadotropin levels gradually decline to reach prepubertal levels by age 1 to 2 years.