how about . . .

How about a mascot that is more cool, and less creepy, than the one you describe. Something like . . . Pedobear.

Seriously, as others have mentioned there are a number of girls in various artforms that more-or-less match your description - but somehow the way you have written it seems kind of creepy to me. "Meet 'Nympho Jenny', a studious young girl who is already considering the significance of her memories of girlhood when she is an old lady! Now appearing in 'Nympho Jenny meets Giant Willie'!" (cue illustration: Nympho Jenny standing next to a Giant)

Otherwise, the theme of children desperately desiring experiences that the adults around them wrongly and stupidly want to thwart - is a staple of literature.