**Core Concept**
A person under a court guardianship, also known as a ward, requires legal protection and management due to their inability to make decisions for themselves. The age at which a person becomes a ward under a court guardianship is essential in medical law and ethics.

**Why the Correct Answer is Right**
In most jurisdictions, a person is considered a minor and thus eligible for a court-appointed guardian until they reach the age of majority. The age of majority varies by country, but it is typically 18 years old in many countries, including the United States and the United Kingdom. This means that a person under a court guardianship would be considered a minor until they turn 18, at which point they would be considered an adult and capable of making their own decisions.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify an age, making it impossible to determine the correct answer.
**Option B:** This option is incorrect because it is not a commonly accepted age of majority in many countries.
**Option C:** This option is incorrect because it is not the age of majority in most jurisdictions.

**Clinical Pearl / High-Yield Fact**
It is essential for medical professionals to be aware of the age of majority in their jurisdiction, as it can impact their ability to provide medical care to minors and their families.

**Correct Answer:** D. 18. The majority is obtained by a person under a court guardianship by the age of 18.