Does my 2 1/2 year old nephew have signs of autism?

[Ashlynn_Rides_Horses04162010]

Hi! Okay, I have a question: in 2014 my nephew was born. He was born 3 weeks early, so he wasn't FULLY developed. He never smiled for 1 1/2 years and never laughed. He has always avoided eye contact, and is VERY interested in spinning objects such as fans. He has separation anxiety, and DEMANDS to be carried EVERYWHERE! If you don't carry him, he throws a tantrum, slamming his fists and feet against the floor, crying without tears. He has a 6 month old Sister, who is already babbling and smiling! He can say things like "mama" and "da-da" and "uh-oh" but it isn't very clear. We are working on teaching him "paw-paw" and it sounds more like "gaaa-GAAA" he goes to a daycare with children his age and older, but usually is by himself, playing. He doesn't show any signs of violence, but I'm confused. Does he show signs of autism? Or is it just delay from being slightly Pre-Mature?