As I have studied McMansions, I found numerous suggestions that aging residents may not want such homes given their current needs. This recent explanation sums up some of the possible issues older residents face:

The McMansion purchased years ago with its acres of ground might now seem too much to handle. With younger family members gone, there may not seem to be so much motivation for larger space. Homes with high balconies and difficult to maneuver staircases present safety challenges. Communities that maintain the grounds can be attractive.

Do the issues older residents face necessarily preclude having a McMansion? In the paragraph above, here are the issues mentioned and the ways McMansions might actually help address these issues:

1. Too much property. Could the McMansion be expanded to take up even more of the property? Or, convert that two-story McMansion into a more sprawling McMansion ranch. While McMansions are sometimes criticized for their size compared to their neighbors, having loss property to maintain could be a plus.
2. Fewer family members in the house so less space is needed. But, Americans love buying more stuff and instead of paying for self-storage a McMansion owner can make use of the extra interior space. They can age in place with all of their stuff.
3. High balconies and interesting staircases could pose problems. Yet, with the space inside a McMansion, could not all of these areas be addressed by renovations? Instead of a twisting staircase, make use of some of that grand foyer to build a straight staircase with a lift.
4. How about more McMansion neighborhoods with HOAs? Millions of Americans already live with HOAs so why not put them to work here making sure grounds and housing exteriors are kept up as residents age?

Sure, smaller spaces might be attractive for seniors but it can be hard to give up space once one has lived with it. There may be plenty of opportunities for older Americans to remain in McMansions if they want to and there are models for how this can be done.