Autism can be diagnosed as early as 12 to 18 months of age, with some signs detectable within the first 6 to 12 months of life. The American Academy of Pediatrics recommends screening all children for autism at 18 and 24 months during regular well-child visits. By age 2, diagnoses made by experienced professionals are generally considered reliable. Early signs include lack of eye contact, not responding to their name, limited use of gestures, and delayed social or communication behaviors. However, some children may not show signs until later, and diagnosis can sometimes be challenging due to the variability in symptom presentation and development rates.