When we speak of creating an aging in place home that someone can find, identify, and then occupy, we really are short-cutting what it takes to make an effective home happen. We are not, as architects or designers, or aging in place consultants taking a sheet of paper and drawing a home plan that we can label an aging in place home and then market it to the masses as such.
An aging in place home that is created without regard for who is going to occupy it and their individual needs is difficult to do. Someone may find a home that meets their specific and anticipated needs, and then again, they may not. Also, at age 50, 60, or 70, someone may seek a home that they can remain living in over time, but they may or may not find it already existing. Someone in their 30s may find a home that they really like that continues to work well for them as they age - with or without significant modifications to it - most people are going to make little tweaks here and there or replace various furnishings, finishes, flooring, lighting, fixtures, or appliances, over time.
Nevertheless, if we mean by creating an aging in place home that we can build a home with mostly universal design features in it - low or no thresholds at doorways, consistent height hard surface flooring throughout, curbless showers, grab bars and seat for use in the bathroom, sufficient lighting, easy access windows and door handles and pulls, modern electronics, low voltage wiring (for lighting, video, gaming, surveillance, and communication), temperature controls, multiple height surfaces in the kitchen, roll-under space in the kitchen and bath, and similar features to these - then it is possible to have a home that works for many, but not all, people as they grow older.
Creating an aging in place home that we could market as such and that people could locate and find in the marketplace would mean that everyone's needs were essentially the same as they age. While taking into account such issues as limited range of motion and reach, reduced vision and hearing, and restricted mobility can be done in designing and building homes, this won't necessarily address everyone's needs. Some people are going to have little impairment as they age, and others are going to have substantially more.
People without urgent needs may find a home they like that they can foresee continuing to meet their needs long-term and thus describe it as an aging in place home. On the other hand, people with a specific condition - or with someone in their household that needs specific modifications - they aren't as likely to find the exact home that is ready to accommodate their abilities without making additional changes to it. There is just such a range of human performance characteristics and physical requirements that it is very hard - if not impossible - to create and market an aging in place home that will appeal to people across the board who are looking for one.
Adapting a home that people want to remain living in that otherwise meets their size and location requirements is relatively easy to do. This is done on a case-by-case basis using the abilities and insights that we have to match a client's specific needs and budget with what we determine will serve them well.