The prevalence of ASD remains relatively stable across the lifespan, necessitating a quantitative understanding of how intervention clinical research is applied across age groups. Here we report a systematic review of treatment studies between 2013 and 2017, enrolling 11,213 subjects with ASD in 218 studies. Individuals under 18 years old constituted the majority of studies (84%) and subjects (92%). Subjects under 18 years old were more likely to be enrolled in behavioral studies (OR (CI) = 1.34 (1.17–1.54)), and less likely to be enrolled in pharmacological (OR = 0.60 (0.52–0.69)) studies than subjects ≥ 18 years old. Identified disparities in both intervention modalities and outcome measures should serve to guide future research priorities.