As a child, my special interests included things like books, rocks, and shells, which most would consider "normal" interests for a young girl. I learned to mask other special interests, like Pokémon, once I figured out that they made me stand out as "nerdy." (Hiding was a common theme of middle and high school.) Books were especially important in my life, as they served as an avenue for learning about the behaviors and feelings of others, and they were also useful as a social barrier to undesirable conversation attempts made by others.
As an adult, I have learned to embrace my nerdiness. The special interest in shells has abated, but rocks are still an important part of my life. I have taken five earth science college courses, and each was a fascinating challenge. When engaging in a camping adventure, I can (and will often) spend an entire day observing and sorting local rocks. Other than the collection of and main interest in rocks, I cycle through periods of intense interest in different areas. Sex was one for a while, although that was mainly while figuring out the whole relationship thing and has diminished by now. Jewelry-making has been an intermittent favorite for years, as well as painting and sculpting. Most days, I am not in the right mood to do most of these. When I am in the mood, I can continue all day, forgoing food and grudgingly succumbing to my bladder.
My special interests to the external world may appear "normal," but that is due to the fact that I have carefully selected the hobbies that are socially palatable to display prominently. I have been hyper-aware of my differences from the majority of the population since I started going to kindergarten, but I just playfully figured that I was an alien or something. I didn't understand the source of the differences until the last couple of years. Since then, my façade of "normality" has fallen slightly, but I am only happier because of it.