Do you know much about the subject of autism?
I know some as I had to do research for it before. It is a developmental disorder characterized by problematic social interaction and communication.
I have an autistic brother and it is difficult for him sometimes. I heard the disorder exists on a spectrum though.
Usually there is a restricted repetitive behaviour.
Hm, so would that mean they do the same things over and over again?
I guess there are set cues or things that set them off leading to a repetitive reaction or action. 
I haven't seen him do that, but I suppose all cases are vastly different.
I just researched it so I'm not doctor. Parents usually notice signs in the first two or three years of their child's life
It's a complicated subject so I wouldn't expect you to know everything about it. My step bother started exhibiting symptoms very young himself.
I guess these signs also develop  gradually but some children do reach the autism milestones at a normal pace.