I think I answered this before, but now, after seeing this thread and thinking more about it...
My first kiss was at 6. Along the same lines as Professor Cool said, while playing house with a girl my mother used to babysit.
First kiss that MEANT something? Umm... 13, or 17, depends on how you look at it.
13 was how old I was when I had my first real girlfriend..
17 was how old I was when I lost my virginity... And she was the only kiss I'd gotten between 13 and 17
Hmm.