Are you interested in Plumbing as a future trade? What are you doing now? Anyway, I started remodeling when I was about 18 and always watched the plumbers and electricians on the job. Its amazing what you can learn by watching and asking questions. Without much info on you, I'd say start with the toilet. Try putting on a new wax ring, or adjusting the amount of water in the tank. Then upgrade to a torch and some solder. You can get alot of info from youtube as well. I know some larger plumbing companies offer weekend classes. Plumbing is a good trade - best of luck to you.
Jeremia