L.R.
Hi! I think you answered your own question well -- "let him be himself and go with it." Eventually he will find other kids his own age whose style of play meshes with his. He may always be more interested in older kids and adults and that may just be his thing.
You're smart to have him in preschool; those years of socialization and learning to follow class rules, move from activity to activity, etc. are so helpful. Have you talked with his teacher there, and is she the one who says he doesn't play with other kids? I find it hard to believe he would have zero interaction; it may be that he isn't doing his "free play" times with other kids much, but he does have to interact with them at times; ask the teacher about that.
Also, he may still be in that stage where kids tend to do more "parallel play" with other children than true interactive play; in other words, they play beside each other but not truly with each other. That's a very normal thing to do and may just last longer for some kids than others.
Do you have one-on-one play dates for him with peers? Try some of that but don't push the idea of playing together too hard. He may be the kind of kid who reacts well to doing a specific activity with another child, rather than being thrown together and told "play with each other," see if he and a friend want to go to puppet shows, children's plays, events at museums, etc. Of course those thiings are all great even if there's not another kid along! Those kinds of activities also may help him open up a bit imaginatively and not want to follow the script of his favorite movies, or life, quite so rigidly, since he can't see or do those things repeatedly and to the same script like he can when he sees the same video over and over.
Be glad you have a mature and probably very smart young guy who is good at interacting with adults; he'll do well as he progresses.