As part of the ongoing effort to make this place a little easier on the eyes...
She's 18 and in that "taking pictures of your feet" phase that arty girls go through. Most of the things that people do in order to "find themselves" are silly, but so are a child's first words. It doesn't make them less cute. And how else are they going to master speech?
Growing an emotional attachment to a girl depends heavily on observing her while she's blossoming from an adolescent into a young adult. The faster a person changes, the more often we have to update our mental profile of them. Since we don't just erase our previous profiles, more frequent updates means a richer record that we have of them, like a wall filled with ticks marking the progression of her height, which accrues hardly any new marks after age 20 or so.
If I know a woman from when she's 25 to 30, I don't need too many pictures to capture how she's changed in appearance (or personality). But to see her development from 15 to 20, I would need a shoebox overflowing with polaroids, just like the ones that parents keep of their children before they reach a certain age. With more pictures for my mind to run its fingers over, the young girl's profile makes me feel that I know her more deeply than someone my own age who I've known for the same length of time.
Fortunately for us, girls don't need to see us change and mature to bond with us -- otherwise 27 year-old women would have crushes on developing teenage boys. They want someone who's already pretty unmovable to stand guard while they're going through their little metamorphosis, when they're least able to protect themselves -- their "I don't care what anyone else thinks" cocoon notwithstanding.
The skin stretched tight over their newly fattened thighs, or large eyes that leap out of their sockets, appeal to the libido -- admittedly a huge piece of falling for someone. But these signals about "look at how I've changed!" threaten a man's psychological independence even more, as a rich record of memories can't be as easily thrown out and replaced as a snapshot of high, supple buttocks. For this reason, you probably still remember your crushes and girlfriends from high school or college more fondly than the last random piece of ass you got.
PS -- anyone who plans to work with teenagers should bear this occupation hazard in mind. Unless you're a grade-A, Angelina Jolie-worshiping girl-hater, the crafty little devils will find a way to get you attached to them. The trick is to get them attached to you too. I was blessed for my interactions on the job with teenagers to have been mostly of the "unspoken love" / "forbidden lust" quality, running in both directions. I can see, though, how other guys would be driven crazy by working with adolescents.