**Core Concept**
The typhoid vaccine is recommended based on the **immunological maturity** of an individual, specifically the ability to mount an adequate immune response to the vaccine. The typhoid vaccine is typically recommended after a certain age to ensure optimal immune response.

**Why the Correct Answer is Right**
The correct answer is related to the age at which the typhoid vaccine is typically recommended, taking into account the development of the immune system. The vaccine is usually recommended after 9-12 months of age for the conjugate vaccine and after 2 years for the oral live attenuated vaccine, as the immune system is more mature.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not align with the recommended age for typhoid vaccination.
**Option B:** This option is also incorrect as the age is not suitable for the typhoid vaccine.
**Option C:** This option is incorrect as the recommended age is not correct.

**Why Each Wrong Option is Incorrect (Continued)**
**Option D:** Given the context, option D is likely "2 years", which could be a plausible answer for the oral live attenuated vaccine but might not be the best choice for all types of typhoid vaccines.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the **conjugate typhoid vaccine** can be given to children as young as 9-12 months, providing earlier protection against typhoid fever.

**Correct Answer:** Correct Answer: D. 2 years.