Not in Australia you can't.
The only way of legally doing Plumbing is via an Apprenticeship.
You can do a Pre Apprenticeship course, but that doesn't allow you to do any Plumbing works unsupervised until you have completed the majority of your Apprenticeship.
You can only do your own works after you have completed your Apprenticeship and become Licensed.
So basically, from when you start your Apprenticeship, @ 5 years later you can legally work for yourself.