**Core Concept**
Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder characterized by persistent deficits in social communication and social interaction across multiple contexts, including verbal and nonverbal communication, and by restricted, repetitive patterns of behavior, interests, or activities. Early signs of autism often appear in the first 2-3 years of life, with significant impact on development.

**Why the Correct Answer is Right**
The onset of autism typically occurs in the first 2-3 years of life, with symptoms becoming more apparent as the child grows and develops. Children with autism may experience delays in language development, social interaction, and repetitive behaviors. However, a diagnosis of autism is usually made before the age of 6 years, as the symptoms become more pronounced and noticeable. This early onset is a key characteristic of autism, distinguishing it from other developmental disorders.

**Why Each Wrong Option is Incorrect**
**Option B:** While repetitive behavior is a characteristic feature of autism, it is not the only option listed, and the question asks for the characteristic that is **not** typical of autism. However, this option is still a valid feature of autism, making it a distractor.
**Option C:** Delayed language development is a common symptom of autism, as individuals with autism may experience difficulties with verbal and nonverbal communication.
**Option D:** Severe deficit in social interaction is a hallmark of autism, as individuals with autism may struggle with social communication, understanding social cues, and forming relationships.

**Clinical Pearl / High-Yield Fact**
A key aspect of autism diagnosis is the early recognition of red flags, such as delayed language development, social withdrawal, and repetitive behaviors. Pediatricians and clinicians should be aware of these early signs and refer children for further evaluation if concerns arise.

**Correct Answer:**
✓ Correct Answer: A. Onset often age of 6 years