This is a rant. It in no way reflects the policies of LJ, or fandom as a whole.
How do we determine underage?
The 18 cutoff seems insane in fandoms like Buffy and Smallville. Especially since Buffy gave it up on her 17th birthday in canon. Someone mentioned it was illegal to depict those under 18 as having sex, because that's kiddie porn.
In that case, Joss & Co., the creators of Dawson's Creek, and every teen sex comedy ever made are all violating the law. So are any after-school specials that deal in pregnancy.
Stephen King gave us 7 twelve year olds having sex (1 girl, six boys) in It.
Heinlein gave us a 15 year old with "romantic fever," (I will Fear No Evil) a 12 giving it away willingly (ibid) a 13 year old coming home announcing "Mum, I guess I'm pregnant" (Friday)
Juliet is canonically 13. Two weeks away from her 14th birthday, and her mother was pregnant at 14 as well.
Judy Blume present 16 & 17 year olds having realistic sex in Forever.
In Chasing Amy, the girl has had a menage a trois before she's out of high school.
I think there is a huge difference between "kiddy-porn" and teen sex. Time Magazine reports that 1/2 of all 16 year olds have had sex. 3/4 have had oral sex and 1/3 have had anal sex.
I think, by insisting all our characters be over 18 before they do ANYTHING is a disservice. And it limits us.
I can see Ron and Hermione stealing a kiss by the time of Goblet of Fire. I can even see Hermione getting swept away by the older Viktor Krumm and making out past a point she's comfortable. (She's 14. My little sister was sleeping around at 14)
I honestly think there's a cutoff at puberty, around 12-13, where anything below should be considered a bad idea (or at least abuse). I think 13-15 is kind of dicey. But I know people who were having babies at that age, and think 16 is too old to be breeding.
I have no problem with 16 and over in explicit sexual situations, esp. if it is established that their society accepts that. Remember, Scarlett O'Hara was 16 at the beginning of Gone with the Wind. She was flirting, flashing her bosom and trying to catch a husband. India Wilkes was a washed-up old maid at 20.
She had her first child before her 17th birthday.
For your consideration, from my college madrigal group:
And I were a maiden c1510
And I were a maiden
As any one is
For all the gold in England
I would not do amiss
And I were a wanton wench
Of twelve years of age
These courtiers with their amours
They kindled my courage
And when I was come to
The age of fifteen year
In all this land, neither free nor bond
Methought I had no peer
The actual sound file Rant over. I think I had a point somewhere.