**Core Concept**
The optimal timing for surgical correction of undescended testis is crucial for maximizing fertility, reducing the risk of testicular cancer, and preserving testicular function. This is based on the principle of maximizing testicular development and histological differentiation.

**Why the Correct Answer is Right**
The best time for surgery is between 6-12 months of age, when the testis is still in the process of descent and histological differentiation is incomplete. Early surgery before 6 months may not be ideal due to the ongoing process of descent, while delaying surgery beyond 12 months may compromise testicular function and fertility potential. The surgery aims to bring the testis down into the scrotum, thereby facilitating its normal development and function.

**Why Each Wrong Option is Incorrect**
**Option A:** Performing surgery immediately after birth is not recommended as the testis may still be in the process of descent.
**Option B:** Delaying surgery beyond 12 months may compromise testicular function and fertility potential.
**Option C:** Waiting until puberty for surgery is too late, as the testis would have already undergone significant histological changes.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the optimal timing for surgery is between 6-12 months of age, and delaying surgery beyond this period may compromise testicular function and fertility potential.

**Correct Answer: C. Between 6-12 months of age.**