Oh no, a twelve year old has found a way to express their budding sexuality in a completely non-harmful and constructive way--WHAT SHALL WE DO? Seriously, would you rather him/her be boning some guy on the street? I'm sorry if humans are innately sexual creatures (most of us, you crazy asexuals you. ;) ) and that develops at different times. If writing is a way for s/he to explore that burgeoning part of his/her personality you have absolutely no right to judge it. It's imagination, it's fiction, and damn it, it's free speech. We don't get denied that until we're 18 and then magically are granted the ability to think/feel/discuss things that are before then societally "inappropriate". Give the kid a break.