Not unusual for boys, whether NT or ND. My friends with social, more NT boys, only started independently reaching out to friends in 8th grade. And they were the social ones. I have other friends with NT boys who socialize outside of school in MS, but it's more a function of other factors - like helicopter parent who still plans everything, or neighborhood boys that don't really need organizing, or even older male siblings who have friends around.
I think the more important questions are: (1) is he happy; and (2) does he have any friends at school. If #1 and #2 are met, you're golden and can stay out of it. If #1 is met, but not #2, you're still probably fine but may want to keep an eye on things, and gently see if you can help without being pushy.