autistic little here
Unfortunately this is too complex of a topic to give you a simple answer online. I got my diagnosis one year ago and it was a struggle for me to know if I was really a little or just autistic. I knew for example how much I care about my plushies but I also knew that that could be just because of the autistic trait of the personification of inanimate objects...
In finding my identity and talking to other autistic people I can tell you that in general autistic people come across as "childish" but don't want to be treated as such, the difference for me was that I do want to be treated as such.
One thing I can tell you for sure, being little and autistic are totally compatible, it doesn't have to be one or the other.
Hope my experience helps!