The aging in place changes that matter most
The bathroom, first. A curbless shower removes the step that causes most falls. Blocking inside the walls for grab bars costs almost nothing while the tile is off. The bars themselves can go in years later.
Getting in the door. A zero-step entry somewhere on the house matters more than most people expect. Usually it comes off the garage. It is also often the single hardest thing to add afterwards.
Doorways and turning space. Widening is straightforward in a frame partition and a much bigger job in block. The US Access Board clearances are a useful reference even in a private home.
First-floor living. In a two-storey house, ask whether a full bathroom and a bedroom fit downstairs. That answer decides whether the house works long term.
Do it early
The worst time to make these decisions is after a fall. Time pressure narrows the choice to whatever someone can install this week. The best time is while a bathroom or kitchen is already coming apart for other reasons.