I couldn't help but giggle when I start thinking about this.
My first was at 5 - he was 6. We were "playing doctor" and were curious what it was like - just before the nanny walked in.
The next one was in 6th grade, shortly before my 12th birthday. My family was visiting one of my cousin's and I couldn't sleep. I was headed outside af ew hours before dawn to do some star gazing. As I opend the door I discovered a guy I liked was crashed on the couch, but not asleep. He joined me outside and that kiss will never be forgotten, though we had no interest in each other when we met years later.