The diagnosis of pneumonia is based on respiratory and systemic symptoms, blood test findings, chest radiographic findings, and the condition of the patient. Physicians in aging or aged societies such as Japan carefully evaluate the comprehensive situation of each pneumonia patient with adequate evaluation and treatment according to "the Japanese Respiratory Society (JRS) guidelines for the management of pneumonia in adults in 2024." These guidelines categorize pneumonia into three types: community-acquired, nursing- and healthcare-associated, and hospital-acquired. The selection of treatment settings and empirical antimicrobials for pneumonia depends on pneumonia classification, severity, and risk factors for potential drug-resistant bacteria, as outlined in the JRS guidelines. This review concisely describes the historical evolution of the diagnosis and treatment of pneumonia in elderly societies, including aspiration pneumonia, from multiple perspectives. In addition, it explores the differential diagnoses when antimicrobial treatment for pneumonia is ineffective, highlighting key aspects through chest radiography and computed tomography.