Few corners, no unnecessary doors, wide paths that let the rooms flow into each other like hallway, [WZ] and kitchen. Bedroom and bathroom close to each other. Built-in wardrobe in the hallway, flush with a main wall. That is the first thing I think of.
What comes to mind spontaneously: no thresholds at terrace doors, handles for windows etc. at sitting height, large parking spaces near the entrance, no doors that are hard to open, maintenance contracts for elevators with fast response times
Do you want to build only barrier-reduced (which is practically every new building) or barrier-free and suitable for elderly/disabled people? If they should be "real" senior apartments, the surroundings are at least as important as the construction method. Often even the decisive criterion. Then you are already heading towards a senior center and should keep things like common rooms or connection to elderly care in mind.
I don't think so. There is assisted living, there are nursing homes. What about couples where one is fit and the other physically disabled? They don't even have to be old. Accident in their 30s, stroke in their 50s.