PC Pookie finished her daily morning washing and jumped to my side. She said that it would be very nice to talk about "old couples".
When a couple is married for long, long years (at least 30) then of course it happens that they don't have any subject to fight about. Everything has been said or done already. On top of this fact, children are out of house and therefore no fights about education, school, outgoing, pocket money and why did you give him/her the car or other kid related things.
So what to do then ? You have to look for a subject. For example you can argue about animals (if you have) in my case cats.
"You forgot to feed the cats". That's a good start, followed by a "No you did" answer (the rest of the discussion would take at least one page).
"Why didn't you let her in/out ?" (the cat) "No, you didn't" etc
"You left the light on ! It never happens to me !" very reproachful voice. Answer :
"What ??? That isn't true, you forget it all the time !"
and it continues with "No you", "No you" until they are both tired and retire in separate corners.
And that brings a little change in their smoothly running days.
Married couples who pretend never fighting are not normal or they are lying, or they are hypocrites, or just simply have nothing to say to each other anymore. And that would be the worst reason.
But usually a nice little healthy fight about such important subjects like crumps laying on the floor, the dishwasher not emptied, the coffee not ready, the post not brought in or it was your turn to bring the garbidge out is good for a marriage. Because then they have to celebrate a reconsiliation, regretting terribly what they both said and usually it ends up with flowers or a restaurant or a movie which is a little changement in the routine of a long married and also mostly retired couple. Of course in earlier times there were other means to reconsiliate ....