In fact, one of the first films to be screened for the public debuted in 1896 and was called The Kiss. Sex scenes are nearly as old as movies themselves. Nowhere near the sex scenes you've seen in movies since you branched out into the R-rated category and beyond. Most likely, it was a movie of the PG-13 persuasion, which you snuck a viewing of far from the eyes of your parents when you were nowhere near the age of 13.
Do you remember the first time you were sexually excited by an image on a screen? ( We do!) It might've been a music video to a teen-pop bop, or a particularly mushy episode of Buffy.