I feel much younger than I am, and I've found that people treat me as being younger than I am. They do it in a protective way, not in a patronizing way.
I heard a psychologist say that every person has an image in their minds of who they are, and this image always comes from a certain stage in their lives. For me, my self-image is that I'm 20. It causes some problems, because I can't do what I was able to do at 20, but that is how I see myself. I think it's what's known as being "young at heart."
But I think there is something about AS that causes this kind of self image to imprint more strongly. Apparently, in NTs, something happens called "brain cell pruning," in which certain areas of the brain atrophy as a person ages. So, when your average NT matures, they go in a linear progression from childhood to adolescence to adulthood. When they reach adulthood, they "put away childish things." The childlike part of their brain atrophies. Aspies, on the other hand, don't lose those parts of their brains. So, while our brains mature, we still retain the childlike parts as well.
This makes total sense to me. I am still a kid inside, even though I'm pretty mature emotionally and intellectually.
I read that when someone asked Einstein how he came up with the theory of relativity, he said something like, "I think like a child, and I ask the questions that a child asks. But I have the brain capacity of an adult man." Apparently, that's textbook Aspie brain development. I don't know how the "experts" figure this stuff out, but that's what I've been reading.