**Core Concept**
The question is testing the understanding of risk factors for hypertension, specifically the distinction between modifiable and non-modifiable risk factors. A non-modifiable risk factor is a characteristic that cannot be changed or modified, whereas a modifiable risk factor can be altered through lifestyle changes or medical interventions.

**Why the Correct Answer is Right**
The correct answer is age, as it is a well-established non-modifiable risk factor for hypertension. As people age, their blood vessels become stiffer, and their kidneys are less efficient at removing excess sodium and fluids from the body, leading to increased blood pressure. This is due to the decreased elasticity of the blood vessels and the increased sympathetic tone with age. The renin-angiotensin-aldosterone system (RAAS) is also activated with age, further contributing to blood pressure elevation.

**Why Each Wrong Option is Incorrect**
* **Option A:** Family history is a modifiable risk factor to some extent, as it can influence lifestyle choices and access to healthcare. While it is a significant risk factor, it is not non-modifiable.
* **Option B:** Obesity is a modifiable risk factor, as it can be managed through diet and exercise. While it is a strong risk factor for hypertension, it is not non-modifiable.
* **Option C:** Smoking is a modifiable risk factor, as it can be stopped through smoking cessation programs. While it is a significant risk factor for hypertension, it is not non-modifiable.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the risk of hypertension increases with age, and it's a major contributor to cardiovascular disease. The American Heart Association recommends regular blood pressure checks starting at age 18, and more frequent checks as people get older.

**Correct Answer:** A. Age