Objective <p>This study examined age-specific utilization patterns and costs of developmental rehabilitation therapy among children with autism spectrum disorder (ASD) in South Korea.</p> Methods <p>A cross-sectional online survey was conducted in November 2024 among caregivers of children under 18 years with ASD. Participants were recruited via online communities for caregivers of children with ASD. Quota sampling was employed to categorize respondents into four age groups (≤ 6, 7–9, 10–12, and ≥ 13 years) based on school age. Only those whose children had received developmental rehabilitation therapy within the past three months were included. Therapy type, frequency, and monthly costs were assessed. Generalized linear models with a gamma distribution were used to identify factors associated with total and out-of-pocket costs.</p> Results <p>Data from 144 children with ASD were analyzed. Children aged 7–12 received the widest range of therapies, whereas adolescents ≥ 13 years received the fewest. Applied Behavior Analysis, the costliest therapy, was most frequently used among children ≤ 6 years. This youngest group also incurred the highest monthly costs (total: US$682.6; out-of-pocket: US$557.7), despite the lowest proportion of government voucher support (7.1%). Younger age and greater disability severity were associated with higher expenditures. Financial burden was the most common reason for planned therapy discontinuation.</p> Conclusion <p>Developmental rehabilitation therapy for ASD shows marked age-related differences in utilization and financial burden. Younger children, particularly those ≤ 6 years, receive more intensive and costly therapies but have the lowest public support. Targeted policy interventions are needed to improve access and reduce the financial burden across age groups.</p>