Also, what type of plumber? residential, commercial, etc....there are different areas that you can specialize in.
Do a google search....here is some info. Not sure how accurate, but you get the idea....
Entry into most of these occupations is through an apprenticeship or, in some instances, a pre-apprenticeship. Plumbing, gas fitting and roof plumbing apprentices complete on-the-job training in conjunction with technical studies through training providers. You have to get so many (hundreds/thousands) hours of on the job training and certification before becoming a "certified" plumber.
The apprenticeship is five years of four levels. Practical and technical training is a minimum of 1800 hours per level. About 80 per cent of the time is spent learning practical on-the-job skills under the supervision of a certified journeyperson and 20 per cent consists of learning the theoretical and technical aspects of the trade through in-school training. The fourth year of training is devoted entirely to acquiring on-the-job experience.