Background Pediatric focal segmental glomerulosclerosis (FSGS) is a heterogeneous disease. Childhood is a dynamic developmental period, and age-related differences may influence disease presentation and progression. However, age-specific clinicopathological features and outcomes remain unclear.Methods We conducted a retrospective cohort study including 305 children with biopsy-proven primary FSGS from Jinling Hospital. Patients were classified into three groups based on age at onset and biopsy, using adolescence as the cutoff: childhood-onset and childhood-diagnosed (COCD-FSGS), childhood-onset and adolescent-diagnosed (COAD-FSGS), and adolescent-onset and adolescent-diagnosed (AOAD-FSGS). Baseline clinical and histopathological characteristics were compared across groups at the time of biopsy. The estimated glomerular filtration rate (eGFR) slope was calculated using a linear mixed-effects model. Renal survival was assessed using Kaplan–Meier analysis, and risk factors for poor renal outcomes were evaluated using Cox proportional hazards regression.Results Three distinct trajectories were identified. The COCD-FSGS group showed early onset, high steroid resistance, and rapid eGFR decline, consistent with an aggressive course. The COAD-FSGS group exhibited the most severe chronic histopathology but had relatively favorable outcomes and slower progression, suggesting a chronic, slowly progressive course. The AOAD-FSGS group presented with more severe baseline clinical features but showed slower decline and better prognosis, consistent with a late-onset, slowly progressive disease course.Conclusions Pediatric FSGS comprises distinct disease trajectories not fully explained by conventional factors. Age may play a key role in shaping disease course. These findings have implications for risk stratification and clinical trial design.