cmg and mayla, the point in this thread is to ask what would be a good age to start not if i should start.
Sorry, imbetter. I misunderstood your question.
Okay, let's reframe an answer for you this way. Conventionally, piano students in degree-granting college programs, study piano pedagogy. Usually a one-semester course where you are familiarized with the various teaching approaches and the leading authors of the books that present that method. You get a beginning student through the music prep department and you teach this kiddo under the supervision of an experienced teacher. After that first kiddo, you may be a prep dept teacher, where you are not directly supervised anymore, but you have experienced teachers around to help you troubleshoot any problems.
So, the pedagogy course is generally required of most piano majors in their second, third or fourth year of schooling. That would make the teacher-in-training typically 17, 18, 19, 20, 21 years of age. Or older, of course.
Could someone younger than this teach? Yes, if they had the maturity and pedagogy training, but such a situation would be rather unusual.
You're a smart guy, imbetter, so if you're the one who wants to teach, take into consideration the above info. Teaching is really very difficult, I think. If you're lame at it, you'll cause damage. So, if you yourself begin teaching, you should hire your teacher to supervise you right off the bat. However, I think you should wait.
If you need cash badly right now, steal hubcaps or something.