I'm a resident of Maryland and my state is Compliant with Real ID, can I still use my old ID to fly?

https://www.dhs.gov/real-id-public-faqs

When will I need to change how I travel domestically?

Starting January 22, 2018, passengers who have driver's licenses issued by a state that is not yet compliant with REAL ID and that has not received an extension will need to show an alternative form of acceptable identification for domestic air travel. Please see TSA's website for a list of acceptable forms of identification. Passengers who have licenses issued by a state that is compliant or that has an extension to become compliant with REAL ID requirements may continue to use their licenses as usual. For a list of states already in compliance or with an extension visit DHS's REAL ID webpage. DHS continually updates this list as more states come into compliance or obtain extensions.

Starting October 1, 2020, every state and territory resident will need to present a REAL ID compliant license/ID, or another acceptable form of identification, for accessing Federal facilities, entering nuclear power plants, and boarding commercial aircraft. This is what we call “card-based” enforcement. The card, itself, must be REAL ID compliant unless the resident is using an alternative acceptable document such as a passport. The Act does not require individuals to present identification where it is not currently required to access a Federal facility (such as to enter the public areas of the Smithsonian) nor does it prohibit an agency from accepting other forms of identity documents other than documents from non-compliant states (such as a U.S. passport or passport card).

Maryland is compliant with the REAL ID requirements, so you can continue to use your old license until October 1, 2020 (or until it expires, whichever comes first).