I had kind of a weird childhood timeline of special interests. As a toddler/preschooler, I had clear-cut obsessive interests. But from middle to late childhood (ages 6-11), I didn't have any stereotypical special interests. But at age 12, I developed my first "rambling/monologue-giving" special interest, and that is the type that I have developed ever since.
My first special interests started around 18 months of age, with Garfield, Full House, and road signs. Pink Panther replaced Garfield when I was about 3, and that obsession lasted until age 5 or so. Science has always been fascinating to me, and I was interested in the human body and organs from as early as age 3. Obstetrics/pregnancy was an unusual special interest that lasted from ages 4-5.
But from ages 6-11, my special interests are harder to define. The only one that stands out is Archie comic books. I collected them during that time, and I had over 700 at one point. I used to read them all the time and line them up and count them periodically. I was also very into Barbie dolls, and I had probably 100 or so. I used to line them up, too. Science continued to be with me, and anatomy/physiology continued to be my favorite area of science. But that's about it.
Then, at age 12, I became "Aspie obsessed" with Cedar Point and roller coaster statistics, and nobody could question my AS diagnosis at that point. 
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Helinger: Now, what do you see, John?
Nash: Recognition...
Helinger: Well, try seeing accomplishment!
Nash: Is there a difference?