In the spring of 1981 I was a 19-year old undergrad at KSU. My FORTRAN professor from a class I had previously completed had to take a two week family emergency leave to deal with a death in the family. The timing was terrible as it was also two weeks before finals when he needed to go. He was not thrilled with the department's grad student substitute he had been assigned that semester for the FORTRAN class, especially given the timing with the approaching finals. As we commiserated over the dilemma, I casually suggested that I'd be thrilled to take over the class for those two weeks.
Engineering FORTRAN was a required class for engineering students, and was typically taken the sophomore year. I had taken mine early as a freshman, since I was in an accelerated program. This would make almost all the students in the class the same age as me, if not little older. It didn't help that in 1981 at the age of 19 I looked closer to 15. Still, he agreed that he would much rather have me help his students out than his grad TA. But since I was just a sophomore, the department and the TA could not know about the arrangement.
The class was held in a huge lecture hall. I arrived early and sat down in the first row to review the textbook and waited for the students to arrive. As the hall began to fill, I got pretty nervous to start the class - that's one reason I didn't start behind the desk or on the dias. A number of the students would recognize me from my work in the computer labs, but for most they would just assume I was another student in the class.
When it was time to start, I closed my textbook and went up beside the desk to address the class. Picture the scene - a lecture hall filled with a hundred or so sophomore engineering students, and this guy who looked to be about 15 stands up to address the class to start teaching - wearing cut-off jeans, a tank top, and sandals, with shaggy hair. As I briefly explained that there had been an emergency and I would be teaching the class for the next two weeks, a stunned quiet fell over the room. From somewhere in the middle of the class came a rather loud, "Oh that is NOT our professor!"
It all turned out fine, and the two weeks went by without incident. The students all did great on their final projects and exam. It was my first introduction to really teaching on a scale larger than in the labs, and I was absolutely hooked. While I've never had a teaching career beyond some guest lectures and leading professional training courses, I've always dreamed of teaching when I retire. At going on 53 now, that is not that far off.