The objective of this study was to determine the clinical features that moderate a later age at ASD diagnosis in females in a large sample of females with ASD. Within two large and independent ASD datasets (>20,000 females), females were first diagnosed with ASD 14-months later relative to males. This later age at diagnosis was moderated by a mild or atypical presentation, wherein repetitive behaviors were limited, IQ and language were broadly intact, and recognized symptoms emerged later in development. Females are at risk for a later age at ASD diagnosis and treatment implementation, and modification of early childhood ASD screening methods for females may be warranted.