Background and Aim Gastric cancer (GC) is one of the most common cancers worldwide, with a high incidence rate in Korean men. However, comparative studies are scarce on the pathologic findings and treatment effects of GC in patients aged less than 40 years. We evaluated the characteristics and pathologic findings of GC patients aged younger and older than 40 years. Methods We retrospectively analyzed 2307 patients diagnosed with GC between January 2010 and May 2018. Eighty‐eight (3.8%) and 2219 (96.2%) patients were younger and older than 40 years, respectively. The patients were divided into younger ( n = 70) and older ( n = 62) age groups through propensity matching. Results Overall, compared to the younger group, the older group ( n = 2219) had a significantly higher proportion of male patients (66.7% vs 39.8%; P < 0.001) and patients who underwent endoscopic submucosal dissection (ESD) (2.3% vs 23.1%; P < 0.001). However, young patients more often underwent operations compared to older patients (78.4% vs 60.1%; P = 0.001). In the propensity‐matched group, older patients more often showed differentiated carcinoma, including well‐differentiated (5.7% vs 11.3%) and moderately differentiated (1.4% vs 32.3%). However, younger patients more often showed signet ring cell carcinoma (SRC) (70.0% vs 25.8%). In multivariate analysis, Helicobacter pylori infection (odds ratio, 12.643; 95% confidence interval, 1.068–1449.665; P = 0.044) independently correlated with SRC risk. Conclusions Patients below 40 years were more likely to undergo surgery compared to ESD, and pathologic findings were more common in SRC. Therefore, more active screening and H. pylori eradication are needed even in patients aged less than 40 years.