I haven't really had an all-encompassing special interest that lasted for any length of time since I was maybe 7 or so (dinosaurs from sometime before I started preschool through first grade, and snakes before that). I think depression may have caused me to not be able to pursue special interests. For the longest time, I didn't have any main interest, other than obsessively reading about certain topics for a couple of days.
Recently, I seem to have more energy to actually pursue interests again. Right now, my "special interest" seems to be classic gaming, but I'm still shifting my focus like every week it seems like (for example, for about a week it was all about emulators, primarily an SNES one, now I'm on actual consoles again, but some days I'm more obsessed with Sega Genesis or Atari 2600 or N64 etc. It's weird). I just bought a bunch of games and hardware, and spent a lot of time getting things out of storage and making room for all my systems, so I hope this interest doesn't fade anytime soon.