My 8 year old daughter has Autism. She did not speak but a few words at the age of 3. With the help of a formal diagnosis of Autism, speech therapy, special ed preschool, resource room assistance, and an IEP in school she has improved drastically. She now speaks non-stop, but sometimes the words are jumbled and don't make sense. When she was almost 4 she was enrolled into the public school special ed program for speech/developmental delays and was given an IEP (Individualized Education Plan) that provided certain goals to reach within a certain amount of time to help her with the delays she exhibited. Through that, the school did an educational diagnosis of Autism which allowed her to have additional services of having a one-on-one aide with her in her classroom. At 5 years old she had a psychological evaluation that determined she has high-functioning mild Autism. She is now 8 and has improved drastically since we initially noticed the delays. She talks, has friends at school that she interacts with, she has eye contact with people, she understands and follows directions and understands consequences, and I could go on and on. When she did not have as much speech/language, at school they used pictures (similar to PECS) to help her communicate better.
Depending on the age and severity of the person you are asking about, they may qualify for services from their local public elementary school. They may also qualify for services through the AZEIP(Arizona Early Intervention Program) or the Department of Developmental Disabilities (DDD). The earlier you get intervention, the better the chances are that their abilities will improve.