Stair Mount Baby Gates for old House

I have just recently moved into an older side by side duplex, in which the stairs run down the wall that is between the two homes. I am having a terrible time finding a gate for the top of the stairs, as the connecting wall is not wood, but cement about 1/4-1/2 inch under the wall board. The bottom of that wall has decorative molding, and the opposite side is 31" tall, but the top 2" is more decorative carving.

All the gates I have seen so far say wood mount only. The problem is, how do I connect a gate to a cement wall when the top of one side and the bottom of the other are different sizes? What brand of gate can be adapted to this situation in a safe way?

Any help would be appreciated. I have tried to research on-line but there is never enough installation info given.

Thanks!!
Denise