Having a quick look via a dummy booking, it looks like 20K is not marked as an emergency exit seat. (In contrast, 21J is.) So it's possible that an elderly/frail passenger would be fine here.

A post in https://www.flyertalk.com/forum/brit...olled-out.html suggests that there's a bulkhead dividing 20A / 20K from the door, which could explain this. It would be good to get confirmation one way or the other from one of our cabin crew members.

See also the video in this post: https://www.flyertalk.com/forum/brit...l#post26303279 - at 0:12 the bulkhead appears to be forward of the door, and 0:21 confirms that the video was taken from 22J looking forward.