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.
We'd need their birthdays, right?