So many autistic people have a low sex drive. It saddens me that it's become a cultural norm to slap a label on that and treat it as an identity. It's usually a product of hormonal imbalance, medication side effects, the part of autism that makes it difficult to connect with people (many autistic people need that connection first to experience sexual feelings) and also just good old autistic burn out. Plus as teens/young people our experiences with human connections are often so different to neurotypical people, even making friends is so difficult so finding someone to have a sexual experience with probably seems impossible.
I think a lot of young 'asexual' people are probably ND, shy, lack confidence and are just, what we used to call, 'late bloomers'
But now they have an 'excuse' for it, I'm not shy/finding dating difficult/just a virgin a little later than the national average...im actually a-sexual. Its like a way for them to opt out of all that pressure and get a nice little pin badge to be part of the LGBTQIA+ crew (how can having no sexual feeling be a sexuality)
Please don't take that as a criticism of your son, I just am talking about the wider scope of the young autistic people in society.
I feel like its the same sort of thing as autistic girls becoming boys. It just feels easier to them to plaster this lable across themselves than to really delve into what they are feeling.