**Core Concept**
The Juvenile Justice (Care and Protection of Children) Act, 2000, defines a juvenile as a child below a certain age threshold, below which a child is considered incapable of committing an offense. This definition is crucial for understanding the legal framework surrounding juvenile justice in India.

**Why the Correct Answer is Right**
The Act defines a child as a person who has not completed eighteen years of age. This definition is based on the United Nations Convention on the Rights of the Child, 1989, which India ratified in 1992. According to the Act, a child is considered a juvenile, and the term is used interchangeably with "child" in the context of the Act.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the JJ Act 2000 specifically defines a juvenile as a child below 18 years of age, not 16.

**Option B:** This option is incorrect because the JJ Act 2000 does not differentiate between boys and girls in terms of age; both males and females are considered juveniles if they have not completed 18 years of age.

**Option C:** This option is incorrect because the JJ Act 2000 does not specify a different age threshold for boys and girls; the age threshold of 18 years applies to all children, regardless of gender.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that the JJ Act 2000 defines a juvenile as a child below 18 years of age, which has significant implications for the administration of justice in cases involving children in India.

**Correct Answer:** A. 18