please help, is my 19 year old autistic?

I am worried about my 19 year old son.  He is lovely, doesn't drink, smoke,swear etc and generally he's a good lad but im worried something is not quite right.  I have always said he's a bit different but because of his good nature i didn't really worry although there have been times over the years when things have seemed more obvious.  Whats currently bought this to attention again is how much he isolates himself.  He doesnt leave the house unless to go and play football which is twice a week,  he mostly only talks to me via text message  even if we are in the same room and mostly if i try and talk to him he will leave the room and text me or just ignore me completely.  He wont answer the phone , Ever and wont answer the door ( i reallly dont know why ) recently he asked me to cook for him at 11.30 at night,  i didnt obviously as i had already cooked at teatime,  anyway i ended up ordering him a kebab but it was really late at this point,  i then fell asleep telling him food was on its way,  i woke up the next morning and my 13 year old explained that when the food arrived my son text him saying open the door the food is here, my 13 year old was asleep so my 19 year old waited for the man to drive off then woke my 13 year old to say why didnt you get the door i really wanted that.  obviously there are several things wrong with that whole situation and honestly i dont understand whay someone would want food, know the food was on the other side of the door yet not answer.  trust me its not laziness,  its a problem.  My son doesnt speak in a normal manner and behaves quite childlike but never aggressive or nasty which is why i cant moan or anything .  he sits in his room almost all day in the dark with a blanket wrappped round his head and is usually biting or sucking his t shirt.  sometimes when he talks its almost like he has a tic as he kind of blurts things out and most of the time when i talk he says shut up idiot to literally everything i say.  i have tried to have conversations with him about what he wants to do with his life and he covers his face,  or hides his face in the back of the sofa.  the other week i had a pack of mince on the side for dinner he put the pack on the floor and said im not eating that then kicked it across the kitchen and he chuckles as he does it as if we are playing,  he really doesnt see that its not normal behavior.  I have tried talking to him but i dont know if he has a clue that things arent quite right.  help