Keep in mind I'm not a Pennsylvanian lawyer and as such I can't guarantee the accuracy of this.
Corruption of a Minor shouldn't really be a concern. The first section of this page
outlines the statutory basis for it and in each case it relates to how old the real person you "corrupt" is. The two relevant sections are (emphasis mine):
(1) (i) Except as provided in subparagraph (ii), whoever, being of the age of 18 years and upwards, by any act corrupts or tends to corrupt the morals of any minor less than 18 years of age, or who aids, abets, entices or encourages any such minor in the commission of any crime, or who knowingly assists or encourages such minor in violating his or her parole or any order of court, commits a misdemeanor of the first degree.
(ii) Whoever, being of the age of 18 years and upwards, by any course of conduct in violation of Chapter 31 (relating to sexual offenses) corrupts or tends to corrupt the morals of any minor less than 18 years of age, or who aids, abets, entices or encourages any such minor in the commission of an offense under Chapter 31 commits a felony of the third degree.
So, corruption of a minor only applies in situations where the actual person you're dealing with (i.e. not their character) is under 18. One quick word of warning though. If the person on the other sign of the screen is under 16 then it is not
a defence to argue that you thought they were 18 or the evidence suggested they were:
(d) Mistake as to age.--
(1) Whenever in this section the criminality of conduct depends upon the corruption of a minor whose actual age is under 16 years, it is no defense that the actor did not know the age of the minor or reasonably believed the minor to be older than 18 years.
That said, that's the risk we all run by being on E. Most laws relating to the sexual conduct of minors/children include a section which holds that if the minor/child is below a certain age then it doesn't matter if you reasonably believed they were over the legal age; you're treated as if you knew they were their actual age.
The more relevant and awkward part is whether writing a story featuring someone under 18 but over 16 is a crime. Visual representations are illegal
on a federal level and the DOJ makes clear that the actual age of consent within your state doesn't matter. To quote them
Additionally, the age of consent for sexual activity in a given state is irrelevant; any depiction of a minor under 18 years of age engaging in sexually explicit conduct is illegal.
But that's visual representations not roleplaying or stories. Pennsylvania's own sexual abuse of children statute
doesn't make clear whether it includes stories/roleplaying. The text itself says (emphasis mine):
Any person who knowingly sells, distributes, delivers, disseminates, transfers, displays or exhibits to others, or who possesses for the purpose of sale, distribution, delivery, dissemination, transfer, display or exhibition to others, any book, magazine, pamphlet, slide, photograph, film, videotape, computer depiction or other material depicting a child under the age of 18 years engaging in a prohibited sexual act or in the simulation of such act commits an offense.
"Other material" could conceivably include stories/roleplays. However the title of that section is:
Dissemination of photographs, videotapes, computer depictions and films
Which indicates it still relates to visual depictions.
One also has to keep in mind Pennsylvania's obscenity.statute
which holds (relevant sections only):
(a) Offenses defined.
--No person, knowing the obscene character of the materials or performances involved, shall:
design, copy, draw, photograph, print, utter, publish or in any manner manufacture or prepare any obscene materials;
Obscene is defined as:
"Obscene." Any material or performance, if:
(1) the average person applying contemporary community standards would find that the subject matter taken as a whole appeals to the prurient interest;
(2) the subject matter depicts or describes in a patently offensive way, sexual conduct of a type described in this section; and
(3) the subject matter, taken as a whole, lacks serious literary, artistic, political, educational or scientific value.
Sexual conduct is defined as:
Patently offensive representations or descriptions of ultimate sexual acts, normal or perverted, actual or simulated, including sexual intercourse, anal or oral sodomy and sexual bestiality; and patently offensive representations or descriptions of masturbation, excretory functions, sadomasochistic abuse and lewd exhibition of the genitals.
(There's quite a funny description of what constitutes "sadomasochistic abuse" but it's not particularly relevant here)
So would a roleplay depicting a 16/17 year old seducing an adult be classified as "obscene". Maybe, maybe not. That's the unfortunate thing with obscenity laws; they're almost deliberately vague and can mean whatever someone wants them to mean. That said the more explicit something is the more likely it is to be classed as obscene; a story which fades to black each time the 16/17 year old and the adult indulge in sexual conduct is less likely to be obscene than one that describes that conduct in detail. Likewise one that makes a big deal out of her age is also more likely to be seen as obscene than one which merely touches on it.
But, keep in mind, we have the Extreme sub-forum on E. When it comes to what may be considered obscene materials I rather suspect that most of the stuff on there is far more likely to fall foul of it then a seduction story featuring a 16/17 year old.
Whether something that is only text can constitute obscenity is still something of an unknown question right now. There have been some prosecutions for it (one of the most famous, Fletcher of Rose Red Stories actually happened in Pennsylvania) but in general they've been pled out relatively early which means there's been no definitive judicial judgement.