Purpose: This study aimed to compare the lung function between the naturally aging lungs (NALs) and diseased lungs, such as chronic obstructive pulmonary disease (COPD) and restrictive lung disease (RLD), in older individuals aged ≥65 years. Methods : This retrospective cross-sectional study included 34 older patients with lung diseases (COPD, n=18; RLD, n=16) admitted to the Rehabilitation Center of CN University Hospital between January 2021 and December 2024 and 25 older individuals with NALs (n=25) in a senior welfare facility. The forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), and FEV1/FVC were measured using a spirometer. The Kruskal–Wallis test was used for group comparisons, and the Mann–Whitney U test was used for post hoc testing. The level of significance was set at 0.05. Results : Only the FEV1/FVC ratio showed a significant difference among the NAL, COPD, and RLD groups. In the post hoc test, the COPD group demonstrated significant differences (p<0.0167) from the NAL and RLD groups. Importantly, the FVC in the NAL group was <80%pred, which was similar to the results of the RLD group, indicating that RLD was due to aging. Conclusion : Lung function declines with age in older individuals with NAL. Therefore, management of NALs is important, although they are not diagnosed with respiratory diseases, because a decline in lung function makes individuals more susceptible to respiratory diseases.