Growing up, I remember my parents disagreeing constantly. Nothing extreme, but they were very different people and often seemed irritated with each other.
Now they are both in their 60s and something has changed. My father cuts fruit for my mother every evening. She reminds him about medicines. They watch TV together and complain if the other person goes somewhere without telling them. Their relationship seems softer than it ever did when they were younger.
Have you also watched your parents' marriage change completely with age?