Purpose: Gastric cancer often occurs in the elderly but is uncommon in young individuals. Whether young patients have different clinical behaviors and outcomes from those of older patients remain unclear. Materials and Methods: We identified 1,366 cases of newly diagnosed noncardia gastric adenocarcinoma from the Kaiser Permanente Northern California Cancer Registry between 2000 and 2010. We then compared the clinicopathological features and survival among the different age groups. Results: The male : female ratio differed significantly between the younger and older patient groups (0.84 in age <50 years vs. 1.52>60 years, P<0.01). More younger patients were Hispanic (54% patients <40 years vs. 19% patients ${geq}70$ years, P<0.0001), while more older patients were Caucasian (49% patients ${geq}70$ years vs. 15% patients <40 years; P<0.0001). The diffuse/mixed histological type was more prevalent in younger patients (70% patients <40 years vs. 27% patients ${geq}70$ years; P<0.0001), whereas the intestinal type was more frequent in older patients (71% in patients ${geq}70$ years vs. 30% in patients <40 years; P<0.0001). Poorly differentiated adenocarcinoma was more common in the younger patients (80% in patients <40 years vs. 60% in patients ${geq}70$ years; P=0.016). Survival rates at 1, 2, and 5 years gradually declined with increasing age (overall P=0.0002). Conclusions: Young patients with gastric cancer had more aggressive disease but higher overall survival rates than older patients. Younger Hispanic patients and older Caucasian patients were more likely to be diagnosed with gastric cancer. These differences may be due to biological predisposition and/or environmental exposure.