Lots of good advice. I'm acyually in the middle of starting my training company.
Best advice I can give is NEVER stop learning. I'm constantly taking classes and improving myself. Once you start teaching you will realize how much you don't know. And you will actually learn alot just by teaching.
Main thing is know your subject. Don't try and teach something that you don't know inside and out. Start by just offering basic safety and fundamental classes, and when your skills an knowledge allow, move on to adding more advanced classes.
As a younger person myself it can be hard to establish respect from older people that are taking from you. You have to establish your authority as an instructor and show that you do actually know what you're talking about. Not in a mean way, but I think you know what I mean. Be confident and speak clearly and with authority. The respect will follow.
Always keep an open mind and always find a way to improve.