One of the specialists who came into school to see an autistic child in my class told me that one early indicator is to call their name and see if they respond. Autism spectrum is very wide and we are all on it somewhere! At this young age it would be very hard to diagnose from the things you have said, as they could apply to a lot of children especially boys! (I am really noticing the difference with my DS's speach and socialising compared to his sisters)