In a cohort of kindergarten children in Ontario, Canada with Autism Spectrum Disorder (ASD) (n = 1522), we tested the association of age at ASD diagnosis and characteristics of (1) the child's primary care provider and, (2) the child using health administrative databases. We tested the association of primary care practice model and time from developmental delay identification to age at ASD diagnosis. Older age of diagnosis was associated with provider foreign training (vs. domestic) (adjusted Hazard Ratio [aHR] 1.17, 95% CI 1.03, 1.33) but not sex, care model, and years of practice. After developmental delay identification, children with paediatricians had longer time to diagnosis than children with providers in care models (aHR 0.68, 95% CI 0.54, 0.86). Findings can be used to inform primary care provider ASD training.