A Mature Mommy's Odd Request

Well, I've been married to my sweetheart for two decades now. We have a lovely house full of laughter and love with our kids who are all grown up and out on their own adventures. Last night though, in the midst of our usual routine, he suggested something quite unexpected. He wanted me to play the role of his little sister for a while, no meaner or harsher tone, just a sweet and innocent little girl act. I found it amusing yet oddly endearing. Is this common among long-married couples? Should we dive deeper into this playful dynamic? Or is it best to stick with our established routine?