Autism Spectrum Disorders is a group of neuro-developmental disorders affecting one in every 100 children worldwide. The cornerstone of ASD management is based on early intervention programs targeted to improve communication, socialization, and behavior skills. This study, conducted at the child development center of a tertiary care hospital in Chattogram city of Bangladesh, aimed to determine the effect of age and other demographic variables on the outcome of early intervention therapy on the improvement of skills of children with ASD. Participants included two groups of children (75 per group) with ASD having different ages - below three years and three to five years. The diagnosis was confirmed using different tools like neurodevelopment assessment form, Bayley scales, M Chat, ICD 10 criteria, and how and why. The intervention was provided on a 1:1 basis and given six subsequent sessions every two months throughout the one-year study period. Statistically significant improvements were observed in different skills in the young age children than in the older group. Almost half of the children (49.3%) from the old age group remained in own agenda stage. On the other hand, all children of young age have significantly improved in early communicator (46.7%), the requester (41.3%), and partner (12%) stages. Moreover, the monthly family income of children posed a significant effect on the outcome of the intervention therapy. The study suggests the initiation of early intervention therapy before age three to get a significant improvement in communication skills of children.