My daughter was diagnosed at 2 I caught the warning signs early. What I noticed in my daughter was her sensory issues, flicking the light switch on and off and playing in her poop and things like that, she would like up all of her books and toys in a row, she would rub her eyes a lot and rarely made eye contact. She didn't like to be held, ran in circles constantly and was super smart when it came to learning. She was way advanced for her age. Taught herself how to do many things. I took her to her doctor and they had me fill out a questionnaire and the doctors referred her to Head Start based on that. They diagnosed her there and she got some extra help and had a few issues with potty training and is still different behavior wise but she's doing amazing in school.