> I would personally want to know as early as possible, so I could get my affairs in order and register my wishes around end of life care and euthanasia while I am still recognised as having full mental capacity.

Everyone should assume that they could lose their full mental capacity at any moment. Strokes, brain injuries, etc. can occur at any age with no warning.

My wife and I finally went through the entire estate planning process several years ago. It was comforting to know that we had a plan for a myriad of scenarios (including the incredibly depressing decision of where our assets would go if our entire family—us and our kids—was gone at the same time).