Why the pedo thing?
Why not make her 18 and keep him 28? They could still have the arc of a screamingly immature *beep* becoming slightly less of an immature *beep* by meeting a very mature girl much younger than him.
His rejection of age appropriate (though still younger) women for this junior high school student is creepy. But he stops himself at the last minute so it's OK, supposedly. Maybe in the sequel Interpol examines CCTV showing him bringing her into his room and he spends the next decade in prison.
I know the actress was 18 or 19 during filming, like the 17 or 18 year old Cheryl Smith playing a 14 year old in Lemora.
I could see this becoming a cult film for pedos - or more precisely, ephebophiliacs. That's not to say that everyone who likes it is. (Nor that anyone involved in the production is.)
To be sure, there is a lot of quality directing, cinematography, acting, writing here. Just hard to get around the icky romance.
Update: I think this analysis is likely a correct inference of the filmmaker's intent:
http://www.imdb.com/title/tt2459156/board/thread/235547973?d=237685159#237685159
Update 2: So completing his arc meant NOT having sex with girl he desired (to self-restraint and concern for others), which meant that she had to be inappropriate for some reason. Still friggin' weird though.