I got it at 16, probably from someone at the restaurant where I after-school waitressed. It sure wasn't from kissing, but I had a hard time convincing my parents of that!
I got it at 16- also NOT from kissing. It was a pretty bad bug. Not only did I flunk all my classes automatically for going over the maximum amount of six days, but it really took me about a year or so to really get over it (also had some relapses.)