Having whined in the past about how 'adult' Will was being portrayed and being smacked upside the head with replies reminding me that some kids were really more advanced than others throughout puberty, I bought into the premise. After reflecting, I decided that yes I did know (remember) some kids who were 14 and easily passed for 18, both back in the dark ages of the early 1960's and when I met some of my son's friends back in 1991 when he was 12. So the story has progressed and Will has become a better understood person based on his history and character as developed by Mark.
I get the feeling, that Kristen turned out to be a much more pivotal character in Gathan's life than Mark originally envisioned and then got stuck in his long range romance, with separation anxiety and all the other angst that goes with trying to maintain a long range relationship. Sometimes, making believeable characters produces some unintended consequences. Life like fiction, happens.
One reviewer opined that the writing got better when the output was not so frenetic and that is probably true, but the writing was never a problem. As I understand it, the problem was where the story was going or not going and that had to be worked out and I think Mark has done a credible job.