I was surprised to find her on the Dick Van Dyke Show because I thought that was so ancient--it was still black and white.
And I thought how much younger she looked than him, but then I considered how Hollywood has always cast younger actresses with older men. Even the Andy Griffith Show, with 2 older single policemen being the stars, had their girlfriends played by much younger women (and I never figured how why they couldn't marry--it would have made a much more interesting plot).
What is more surprising is that Dick Van Dyke is still alive--at 91 years old, which means there was only an 11 yr difference between them on the show.

And that is assuming we are talking about getting married. How many couples out there are 'living in sin' even retirees who get more money from Social Security if they do not marry, and do not have all the complications of which offspring receive which assets when they die.
I don't even know if the Census Bureau has made a count of all the couples living together without being married. It would be hard to do since many adult children still live with their parents.
I saw an advice column in the newspaper with a question from a 50 year old man living with his mother, asking about how to get his nephew to learn proper table manners. I thought the question should be--is it time for me to leave my mother's house?