**Core Concept:** Universal Health Insurance (UHI) is a health financing strategy that aims to provide financial protection and access to health care services for all individuals in a population. The scheme guarantees a minimum package of health services without exposing the beneficiary to the risk of unlimited medical expenses. Age limits may vary across different UHI schemes, but the question focuses on the most common scenario.

**Why the Correct Answer is Right:** In most UHI schemes, age limits are set to ensure the scheme's sustainability and efficiency. Typically, there is a lower limit to protect the young and healthy individuals from subsidizing the care for the elderly and vulnerable population. The upper limit is set to prevent excessive health expenditure on a few individuals, ensuring the scheme remains financially viable for the government or payer.

**Why Each Wrong Option is Incorrect:**

A. **Lower limit (Option A)**: This is often set around 60-65 years, ensuring enrollment of the majority of the population (e.g., 65 years in India's Ayushman Bharat scheme). Lowering the limit too much may put a strain on the scheme's resources.

B. **No upper limit (Option B)**: Setting no upper limit would lead to an increased burden on the scheme and could destabilize its financial stability. The scheme would have to bear the cost of the oldest and most expensive group of individuals, which could cause financial distress.

C. **No age limit (Option C)**: Similar to option B, this would compromise the scheme's financial stability and lead to an unequal distribution of costs and benefits among scheme participants.

D. **Upper limit set too low (Option D)**: An upper limit set too low would result in the exclusion of a significant portion of the population, negatively affecting the scheme's coverage and effectiveness.

**Clinical Pearl / High-Yield Fact:** Ensuring an appropriate balance between lower and upper age limits is crucial for the success of a UHI scheme. Striking the right balance between the age limits ensures the scheme is financially sustainable, covers a substantial portion of the population, and provides equitable access to healthcare services.

**Correct Answer:** C. No age limit (Option C)

In the context of UHI schemes, setting an age limit too high (Option A or D) or too low (Option B or D) would compromise the scheme's effectiveness and financial stability. Option C, "No age limit," ensures that the scheme covers the entire population, providing equitable access to healthcare services for all age groups. This allows for a more comprehensive coverage of health needs and reduces the financial burden on the scheme.