not interested? or not being able to? it starts to look like a diagnosis (as an extreme illustration Rain Man comes to mind). It is not a big stretch of imagination to allow that after 20 years of being in the same situation an elderly person may lose ability for "changes", just like many lose ability to bend and reach the floor or make a split. Brain is just a biological organ and there is a lot of information around about it losing its "flexibility" with time.
Basically the society is very cruel to its members who lose the ability to function above specific level, be it physical or mental abilities.