PA juvenile criminal laws

If you want to save your friend a lot of trouble, DO NOT HAVE SEX WITH HIM!! Even though it may be legal, it sounds like your parents intend to make trouble for him. In fact try not to be alone with him until you are at least 16.

The following from Wikipedia seems to be the law in Pa.:

The age of consent in Pennsylvania is 16 years of age. Teenagers aged 13, 14 and 15 may legally engage in sexual activity with partners who are less than 4 years older.

It is very clear that there are no laws that directly criminalize any consensual non-coerced sexual conduct with any person the age of 16 or older unless certain mental issues are present (mental retardation). [8]

Maybe it is time to sit your friend down with your parents and have an open discussion with all present as to what they expect and what you are up to and how you can make them feel more comfortable with your "relationship".

If that is not possible to do on your own, do it with the help of a school guidence counselor or a trusted teacher or even a clergy member.
Believe it or not, a good family lawyer could do this well for you to, but it might be expensive.

Good luck.

Parents do not have the power to have other juveniles detained or placed into the custody of authorities. However, this does not mean that the will be precluded from calling the police requesting an investigation begin into potential violations of the PA Crimes Code.

You are fortunate to have parents who apparently care about your well-being. Perhaps you should consider their concerns.

Your parents cannot place anyone in jail. A person can only be arrested by the police, charged with a crime by a prosecutor, and sentenced by a judge if they are found guilty of the crime, or adjudicated delinquent by a juvenile court judge.
Your parents could report your friend to the police, who could investigate and charge him with crimes. If he is found guilty or adjudicated delinquent, one of the possible penalties is confinement in an adult or juvenile facility.
It is illegal to have sex with a 13 year old just about everywhere in the world, even if the 13 year old consents or the parents consent, or anyone else consents, unless the 13 year old is married to the sex partner (this is a very rare situation).