Late to speak (but only just, you know, reaching the absolute minimum number of words expected by any given age, therefore making the professionals think she was just a slower bloomer than most).
Not interested in peers from a very young age. Other children wanted to smile at each other, play alongside etc, she just scowled at other children and did not want to share anything with anyone (was put down to her personality by anyone I commented to about it).
Preschool finally noticed she never really grew out of the playing alongside stage, she never had much shared imagination, whereas all the other little girls were roleplaying at every opportunity. She also referred to herself as "you". Still told by professionals she would likely grow out of it.
Now, in reception, she is just different, and the teacher notices it. She still struggles with shared imagination play, and her social communication skills are clumsy at best. She does not read people or social situations well at all, and can be behave oddly as a result. As she is only 4, it is not tooooo obvious to her "friends" so she still has some at the moment. Not so sure this will last though.
I thought she was different from about 12 months, for all of the above reasons, but have oscillated between being very sure she is autistic, and thinking, no, she will out grow it all and be fine.
I am in the diagnostic process, but I think it might take a while for her to be given a diagnosis. She does not seem to have any of the fixed patterns of thinking that are required for a diagnosis. No issue with routine change, no repetitive actions or play, no obsessions. She could just have sensory processing and social communication disorders rather than a full diagnosis of autism. I will have to wait and see.