[LittleRedToyota]

you can open carry if 18 or over by virtue of the fact that the PA UFA only makes it generally illegal for someone under the age of 18 to possess a firearm.

§ 6110.1. Possession of firearm by minor.
(a) Firearm.--Except as provided in subsection (b), a person
under 18 years of age shall not possess or transport a firearm
anywhere in this Commonwealth.
(b) Exception.--Subsection (a) shall not apply to a person
under 18 years of age:
(1) who is under the supervision of a parent,
grandparent, legal guardian or an adult acting with the
expressed consent of the minor's custodial parent or legal
guardian and the minor is engaged in lawful activity,
including safety training, lawful target shooting, engaging
in an organized competition involving the use of a firearm or
the firearm is unloaded and the minor is transporting it for
a lawful purpose; or
(2) who is lawfully hunting or trapping in accordance
with 34 Pa.C.S. (relating to game).
(c) Responsibility of adult.--Any person who knowingly and
intentionally delivers or provides to the minor a firearm in
violation of subsection (a) commits a felony of the third
degree.
(d) Forfeiture.--Any firearm in the possession of a person
under 18 years of age in violation of this section shall be
promptly seized by the arresting law enforcement officer and
upon conviction or adjudication of delinquency shall be
forfeited or, if stolen, returned to the lawful owner.
(June 13, 1995, 1st Sp.Sess., P.L.1024, No.17, eff. 120 days;
Nov. 22, 1995, P.L.621, No.66, eff. imd.)