B737-800 Captain reported left aft entry door warning on takeoff resulted in a rejected takeoff.

Narrative

Rejected takeoff at 117 kts. (158;000 lbs.) due to L AFT ENTRY DOOR light.Reject at approximately 2500 ft. on takeoff roll; AUTOBRAKES engaged; easily exited the runway at 'E' Taxiway. Cleared the runway; stopped on the apron for brake cooling. Taxied to the gate and shutdown.Called for Maintenance inspection and to balance my AML writeup. Called Dispatch to get a new release and check fuel (No additional fuel required). 7 passengers decided to deplane.Queried Flight Attendants about what they did to secured aircraft doors. I was informed that they all 'pushed' the handles down. All light were extinguished; from push back to takeoff roll.Explained to the FA's (Flight Attendants) this is a good example of the importance to 'push' the door handles down after doors are closed.Possible 'sensor' switch in door handle that illuminated the L AFT ENTRY DOOR light. For the 737; insure FA's are briefed on the importance of pushing the door handles down after doors are closed. This is already emphasized by Company's training department.