It shouldn't matter whether or not the license is expired. It is still your identification. TSA isn't going to give you a ticket for 'flying with and expired driver's license'. (I hope).

Your expired license still shows a picture of you, with all your information, and if they are really ambitious, they can call PA DMV and verify that, yes, you have a valid license.

My AK Driver's License does the same thing. Since I'm active duty military, I don't have to renew it until after I get out of the Army. The expiration date says 1997, but it is valid until 90 days after I get out. I think only two car rental places have even made any kind of comment, and one was in Germany.