Reflecting on my thought processes at that age, I remember it being entirely about 2 things:
1. Expression. Nothing could have sounded more dull than building aimlessly-- I wanted to DESIGN. (My definition of this being "carrying out a specific communicative purpose through look and function.") I wanted to make a website that demonstrated my tastes and values to my friends. (Which is likely why I went straight to websites and not desktop software.)
2. Social dynamics. Similar but different to the aforementioned point, I wanted to actually affect other people with what I was making. As a young girl, that typically meant impressing potential friends and boyfriends. I had a poetry site at one point. I made sites for a fake band my girl friends and I talked about forming. I had tons of blogs. I really should have segued into games at that time, as that would have fallen in the same category, but sadly I did not.
While I know every human being is different, I was what you'd consider a "girly girl." So I believe the difference between myself and a young boy was quite pronounced in a stereotypically feminine direction-- which is where one should be investigating a subject like this, in my opinion.