**Core Concept**
Klinefelter's syndrome is a genetic condition affecting males, characterized by the presence of one or more extra X chromosomes in addition to the typical XY pattern. This leads to a range of physical and developmental abnormalities.

**Why the Correct Answer is Right**
Klinefelter's syndrome is caused by a non-disjunction event during meiosis, resulting in the presence of XXY or other variations of extra X chromosomes. Individuals with Klinefelter's syndrome typically exhibit tall stature, gynecomastia, and reduced fertility due to Sertoli cell dysfunction and impaired spermatogenesis. The condition is also associated with an increased risk of autoimmune disorders, such as Hashimoto's thyroiditis and systemic lupus erythematosus.

**Why Each Wrong Option is Incorrect**
**Option A:** While individuals with Klinefelter's syndrome may exhibit some features of feminization, they do not typically undergo a complete sex reversal and develop female external genitalia.
**Option B:** Klinefelter's syndrome is not associated with a specific age-related onset, but rather is a congenital condition present from birth.
**Option C:** While individuals with Klinefelter's syndrome may have a higher risk of certain medical conditions, they do not have a significantly increased risk of developing a specific type of cancer.

**Clinical Pearl / High-Yield Fact**
Individuals with Klinefelter's syndrome often exhibit a characteristic "marfanoid" body habitus, with tall stature, long limbs, and a slender build.

**Correct Answer:** C.