Chronic kidney disease (CKD) is a growing global health challenge, with smoking identified as a significant risk factor. This study investigates the long-term impact of adolescent smoking initiation on end-stage kidney disease (ESKD) development. A retrospective cohort study was conducted using data from the Korean NHIS claims database. The cohort included 201,678 CKD patients aged ≥40 with a documented smoking history. Patients were stratified by smoking initiation age (<20 vs. ≥20 years) and cumulative smoking exposure (pack-years, PY). The primary outcome was ESKD incidence, defined as kidney replacement therapy initiation. Cox proportional hazards models assessed the relationship between smoking initiation age, smoking burden, and ESKD risk. During a median 6.8-year follow-up period, 6,334 patients progressed to ESKD (IR, 3.63 per 1000 person-years). Those with higher PYs were older and had more comorbidities, such as hypertension and diabetes. Patients who began smoking before age 20 and accumulated ≥20 PYs had a significantly higher risk of ESKD (HR, 1.26 [1.16-1.38]) compared to those with the same exposure but later smoking initiation. Increased cumulative smoking exposure further elevated the risk. When PYs were divided according to initiation age, a higher ratio was associated with an increased risk of ESKD. Early smoking initiation during adolescence was associated with a significantly higher risk of progression to ESKD in patients with CKD, especially in those with higher cumulative smoking exposure. Public health interventions focusing on preventing adolescent smoking can mitigate the long-term burden of CKD progression.