You will probably become a digger and a plasticer first. Plumbum isn’t in use much any more. Go to the local supply house and look on the boards for a helper position. Ask plumbers. Find the local union members and ask. Inquire at the State employment office for training. Look at the county vocational college and school course list for classes.
Try a pre apprentice course at tafe(if you live in oz) a lot of employers look for this when taking on new apprentices, it can also go as a credit to the theory side of your apprenticeship