**Core Concept**
The development of the lens in the eye involves the formation of different nuclei at various stages of embryonic development. The lens grows throughout life, and its structure is composed of different layers formed at different times. Understanding the development of the lens is crucial in diagnosing and managing lens-related disorders.

**Why the Correct Answer is Right**
The infantile nucleus is not completely formed by one year of age. The lens develops in the following stages: the embryonic nucleus is formed between 3-8 weeks of gestation, the fetal nucleus is formed between 8-35 weeks of gestation, and the infantile nucleus is formed between 35 weeks of gestation and 1-2 years of age. Therefore, the infantile nucleus is still under development and not fully formed by one year of age.

**Why Each Wrong Option is Incorrect**
**Option B:** The embryonic nucleus is actually situated between the two Y sutures, which is correct. This is where the embryonic nucleus is formed during the early stages of lens development.
**Option C:** Congenital blue dot cataracts are associated with a high risk of developing senile cataracts, but this is not necessarily at an early stage. The development of senile cataracts is a gradual process that occurs over many years.
**Option D:** Zonular cataracts typically affect the outer part of the fetal nucleus or the inner part of the adult nucleus, which is correct. Zonular cataracts are a type of cataract that affects the lens fibers in a specific zone.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the lens continues to grow and develop throughout life, and its structure is composed of different layers formed at different times. This knowledge is crucial in diagnosing and managing lens-related disorders, such as cataracts.

**✓ Correct Answer: A. The infantile nucleus is completely formed by one year of age**