Can I still use my Pennsylvania drivers license to board a domestic flight at BWI?

Yes

According to thr Department of Homeland Security website. Pennsylvania has an extension for REAL ID enforcement, allowing Federal agencies to accept driver's licenses and identification cards from Pennsylvania at Federal facilities, nuclear power plants and federally regulated commercial aircraft until August 1, 2019.

Yes you can .😀

Yes. https://www.tsa.gov/travel/security-screening/identification