**Core Concept**
The distribution of body fluids between the intracellular fluid (ICF) and extracellular fluid (ECF) compartments changes significantly throughout life. Understanding these changes is crucial for assessing fluid balance and electrolyte disturbances in clinical practice.

**Why the Correct Answer is Right**
The ratio of ICF to ECF volume approaches adult levels at approximately 12 years of age. At birth, the ICF compartment is relatively small compared to the ECF compartment due to the high water content and low protein concentration in the newborn's tissues. As the child grows, the ICF compartment expands, and the ICF to ECF ratio increases, eventually approaching the adult ratio by around 12 years of age. This change is due to the maturation of the capillary bed, increased muscle mass, and changes in the composition of body fluids.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the ICF to ECF ratio does not approach adult levels at birth. The newborn's ICF compartment is relatively small.
**Option B:** This option is incorrect because the ICF to ECF ratio does not approach adult levels until around 12 years of age.
**Option C:** This option is incorrect because the ICF to ECF ratio does not approach adult levels until the child reaches adolescence.

**Clinical Pearl / High-Yield Fact**
Understanding the changes in body fluid distribution throughout life is essential for assessing fluid balance and electrolyte disturbances in pediatric patients. Clinicians should be aware that the ICF to ECF ratio is not the same in children as in adults and adjust fluid management and electrolyte replacement accordingly.

**Correct Answer: C. 12 years of age.**