Hey, you and I are the same age! Okay, I was thinking maybe you were younger and your folks not much older than I, so I was like, "What's creepy?" to sort of tease you in defense of older folks (like me) as sexual beings. But I hear ya about being surprised. For myself, it's not something I would be creeped out about necessarily, my mother was pretty open about her sex life as far as us knowing she had sex anyway (she was divorced, so had boyfriends).
In my family, I found out in my 30s that the "boarder" who lived with my great-grandparents was actually my great-grandmother's boyfriend. Apparently, it was common knowledge when I was little, according to one of my grandmother's cousins who told me. Both my ggparents died by the time I was 12, but I only found out about Oscar's true place in their lives about 25 years after they passed away. They were in their 70s when he lived with them, and I remember him well. So, they were a in a Vee into their twilight years!