I'm asexual. Not autistic. No medication. No hormone issues and certainly not a "cultural" thing.
I'm 48, I've known I'm asexual from about the age of 13 when all my peers started fancying boys. Although I didn't learn the term asexual until my mid 20s.
I think a lot of young 'asexual' people are probably ND, shy, lack confidence and are just, what we used to call, 'late bloomers'
You know asexuality isn't actually about who you date but who you're (not) attracted to? Plenty of ND/shy etc people have crushes or are attracted to people.