I began planning for old age 40 years ago - when I bought this house. It has a self contained one bedroom basement suite. The suite was the teens' introduction to living alone - cook/shop, keep suite tidy and clutter free, weekly inspection from the POLICE (aka Mom).
I planned to move into the suite when I can't manage the stairs and when the current living area is too large for me. The spare bedroom is in use when my daughter, sons, grands visit. As I get older, there will be more visits to make sure "mom" behaves.
Currently, the 4 bedrooms are in use -
#1 for the dog and I;
#2 sitting/TV room with a pull out bed if grands come with their parents;
#3 the office and pantry/"junk room" ;
#4 for the children/grands when they visit;
The self contained basement suite was/is rented to "off shore" university students as I find it more interesting to interact with students from other countries. The rent is lower than normal as I prefer NOT change tenants yearly. At close proximity to public transportation and the university, there has never been a problem renting the suite.