Is it legal to ride a gas powered pocket bike in Philadelphia?

Where I live, that would be a negative. You cannot ride any motorized vehicle of more than 50ccs on the street without having your learner's permit and taking a moped class. If you are 16 and have your full licence, you still have to have a motorcycle licence and the bike has to meet certain standards. (has to have headlights, turn signals, etc.) So unless you can find somewhere to ride it where you have enough space and don't have to trespass, I'd recommend finding a new hobby.