ImportanceThe introduction of immune checkpoint inhibitors (ICIs) has transformed the care of advanced non–small cell lung cancer (NSCLC). Although clinical trials suggest substantial survival benefits, it is unclear how outcomes have changed in clinical practice.ObjectiveTo assess temporal trends in ICI use and survival among patients with advanced NSCLC across age strata.Design, Setting, and ParticipantsThis cohort study was performed in approximately 280 predominantly community-based US cancer clinics and included patients aged 18 years or older who had stage IIIB, IIIC, or IV NSCLC diagnosed between January 1, 2011, and December 31, 2019, with follow-up through December 31, 2020. Data were analyzed April 1, 2021, to October 19, 2022.Main Outcomes and MeasuresMedian overall survival and 2-year survival probability. The predicted probability of 2-year survival was calculated using a mixed-effects logit model adjusting for demographic and clinical characteristics.ResultsThe study sample included 53 719 patients (mean [SD] age, 68.5 [9.3] years; 28 374 men [52.8%]), the majority of whom were White individuals (36 316 [67.6%]). The overall receipt of cancer-directed therapy increased from 69.0% in 2011 to 77.2% in 2019. After the first US Food and Drug Administration approval of an ICI for NSCLC, the use of ICIs increased from 4.7% in 2015 to 45.6% in 2019 (P < .001). Use of ICIs in 2019 was similar between the youngest and oldest patients (aged <55 years, 45.2% vs aged ≥75 years, 43.8%; P = .59). From 2011 to 2018, the predicted probability of 2-year survival increased from 37.7% to 50.3% among patients younger than 55 years and from 30.6% to 36.2% in patients 75 years or older (P < .001). Similarly, median survival in patients younger than 55 years increased from 11.5 months to 16.0 months during the study period, while survival among patients 75 years or older increased from 9.1 months in 2011 to 10.2 months in 2019.Conclusions and RelevanceThis cohort study found that, among patients with advanced NSCLC, the uptake of ICIs after US Food and Drug Administration approval was rapid across all age groups. However, corresponding survival gains were modest, particularly in the oldest patients.