My first was when I was around 7 or 8, it was interesting for a few other reasons besides just being lucid for 1 second.

I had a dream where I was playing around in bed thinking about the TV show Recess, I had a false awakening, looked over the edge of the bed, saw my clock turn into a mermaid, my little brother started eating my arm, I realized it was a dream and opened my eyes.

What made it interesting was that the time on the clock was the same in my dream and in real life, and I woke up in the position I was in the dream.