Background The optimal treatment strategy for elderly patients with gastric cancer is still controversial. This study aimed to assess the impact of age on short- and long-term outcomes after treatment for primary gastric cancer. Methods From January 2004 to December 2014, a total of 507 patients underwent gastrectomy for gastric adenocarcinoma at two high-volume upper gastrointestinal (GI) centers. The patients were classified into three groups as follows: group A (patients ≤ 69 years old, n  = 266), group B (patients 70–79 years old, n  = 166), and group C (patients ≥ 80 years old, n  = 75). Clinicopathologic characteristics as well as, short- and long-term outcomes were compared between the groups. Results The patients in groups B and C had more comorbidities, whereas the younger subjects (group A) had more advanced tumor stages. Less extensive surgery was performed in the groups B and C. Older patients (age ≥ 70 years) had more postoperative medical complications. Moreover, group C had a higher postoperative mortality rate (8.1%) than group A (1.8%) or group B (1.9%). In the multivariable analysis, age older than 80 years (group C) was a negative independent factor for overall survival (OS) (hazard ratio HR, 2.36) compared with group A, whereas group B seemed to have a comparable risk (HR, 1.37). Notably, the three groups did not show significant differences in disease-related survival (DRS). Conclusion The data suggest that patients 70–79 years of age show a risk of postoperative death comparable with that of younger subjects. However, patients older than 80 years should be carefully selected for surgical treatment due to the increased risk of postoperative mortality.