Pennsylvania Consolidated Statutes
CRIMES AND OFFENSES (TITLE 18)
ARTICLE B. OFFENSES INVOLVING DANGER TO THE PERSON.
CHAPTER 31 - SEXUAL OFFENSES
§ 3122. Statutory rape (Repealed).
§ 3122.1. Statutory sexual assault.
Except as provided in section 3121 (relating to rape), a person commits a felony of the second degree when that person engages in sexual intercourse with a complainant under the age of 16 years and that person is four or more years older than the complainant and the complainant and the person are not married to each other.
He probably won't face statutory sexual assault charges simply because they have murder and kidnap now.
It would be greek tragedy if one of his motivations was that the parents had threatened him with statutory charges that he wouldn't have actually even been liable for under PA laws.
I'm guessing that they count by number of months. 48+ months older and you can be charged. 47- and your safe. Seems stupid, but they have to draw the line somewhere.