Also forgot to say - all of the characteristics of ASD will be found in some neurotypical people (including lack of empathy, difficulty with social interaction, lack of social imagination, over or under sensitivity to stimuli such as noise, rigidity of habit... etc) . None of them on their own means a person is autistic - it is the constellation of all the features, and the impact they have on the person's life, which indicates they are autistic.
When DS was around 2/2.5 years old, and I was starting to worry about him, I could rationalise literally everything I saw with 'lots of kids do that'. And they do! It was doing all of those things, as much as he did, and for so long in terms of where he should have been developmentally, that was the cause for concern.
Anyway, he is coming along very well st the moment, although with his improved ability to communicate comes assertiveness and the need to test boundaries. We are having challenging behaviour now (delayed terrible twos maybe!) that isn't, I don't think, his autism but just normal growing up stuff. However, his reaction to our response is flavoured by his ASD so that is keeping me on my toes!