I can't remember exactly how old I was when I got my first sex talk, but I do remember it well. It was in the afternoon, and it was wintertime. I was with my dad behind the milking barn helping him fix the tracks that spread silage from the silo down the feeding trough for the cows as they were lining up to be milked. My "helping" at this age amounted to standing at the ready to fetch a wrench or whatever dad needed, so I had a lot of time to stare out into the distance.
As I was staring out into the field, I noticed two cows acting kinda funny towards each other, and I said, "Hey, Dad, look at those two cows wrestling!" And my Dad said, "Well, son, those cows aren't wrestling. They're having sex." To which I inquired right on queue, "Sex, what's that?"
"Well, sex is where babies come from," my dad told me, and he then proceeded to give me the whole biological breakdown of mammalian reproduction in broad strokes: penises, vaginas, sperm, eggs, fertilization, pregnancy, delivery. Up until that point, I'd never really given any thought to where babies came from, and the whole process seemed so wholly complicated and involved that it kinda blew my mind. "Cool!" I seem to recall saying, which got a chuckle out of my Dad. I would have never guessed it had he not told me.