**Core Concept:** Paget's disease is a common disorder that affects the bone and is characterized by abnormal bone remodeling, leading to bone pain, fractures, and deformities. The disease is associated with increased bone resorption and impaired bone formation.

**Why the Correct Answer is Right:** Paget's disease primarily affects individuals in the elderly population, as it is estimated that it occurs in approximately 3% to 5% of those aged 50 years and older. The disease is caused by genetic mutations in the protein kinase domain of the SQSTM1 gene, leading to increased osteoclast activation and impaired osteoblast function. Osteoclasts are responsible for breaking down bone tissue, while osteoblasts are responsible for building bone tissue. When osteoclast activity is increased, bone remodeling is accelerated, resulting in bone resorption and increased bone pain.

**Why Each Wrong Option is Incorrect:**

A. Although Paget's disease can affect individuals of any age, the correct answer is still the elderly population as the prevalence increases with age.

B. While the disease can affect people of any sex, the correct answer still refers to the age group most commonly affected.

C. Paget's disease can affect individuals in their 20s and 30s, but the question specifically asks for the age group most commonly affected, which is the elderly population.

D. Similar to option C, this option also focuses on the disease affecting young individuals, whereas the question asks for the age group most commonly affected, which is the elderly population.

**Clinical Pearl:** Paget's disease is often asymptomatic and may be discovered incidentally on imaging studies or laboratory tests. However, when symptoms do occur, they include bone pain, bone deformities, fractures, and neurological complications such as balance issues and dementia. Early diagnosis and treatment can help prevent complications and improve patients' quality of life.