Rather than trying to define a specific type of living space as the ideal for someone who wants to remain living in their home, we need to focus more on making that home safe, comfortable, convenient, and accessible for those living in it.
While there are several types of aging-in-place solutions that we would like to see implemented - if they are not already present in someone's home - aging-in-place does not revolve around a set pattern of solutions. Some may be more indicated than others, and it is based on what someone needs rather than just equipping a home with a boilerplate list of solutions.
While an accessible and visitable entrance, wider doors, lever door handles, single lever faucets, rocker light switches, lower thresholds, easy-entry showers, generally lower wall controls and switches, and easy-to-open windows and cabinetry typify aging-in-place that often are recommended, it still needs to be based on what will serve the specific occupants of a home we are designing for - and what already might be present that does not need to be added.
There definitely can be a systematic approach to evaluating and determining key components of an aging-in-place renovations, but just going with a standard list of of commonly used improvements is not necessarily taking into account the needs of each individual household.
True, in the absence of any of the normal types of recommended improvements and solutions already being present, these approaches would seem to be the minimum of what we might recommend, but the personal tastes, desires, physical requirements, priorities, and budget of a specific household may suggest otherwise and not require this strategy. It could need less of a treatment or even more.
The main thing to remember is that we are working with individual with their specific needs and particular desires to maintain their dignity and way of life - even if that does not conform to what we think should be present or what we would like to see installed for them to make their lives easier and more pleasant. It is their home, and they have they right to maintain it the way they want unless they are safety or health concerns present that we need to step in to resolve.
A careful assessment of the needs of the people we are designing for, the physical age and condition of their home, physical constraints of that home for being to enact various changes (without significant construction or budgetary issues and concerns), and how people feel about making changes to their home are going to govern our efforts more than just trying to incorporate some commonly accepted list of improvements.
Some improvements that we are going to suggest and want to make are going to be based on the style of the home and when it was originally built. Even at that, some of those improvements are going to be much harder to accomplish, more expensive and extensive in their nature, and more disruptive to the daily schedules of those living the home than what may be practical or acceptable.
That's why aging-in-place solutions are done on a case-by-case, home-by-home approach and not rolled out as a mass project.