I have been actively repairing computers for the last 16 or so years and I have just recently (within the last 5 years) been able to claim the title of “Tech”, but since I don’t have a piece of paper that says I have completed a course of study, I can’t get a serious computer repair job unless I open my own shop.
So… if you want to take the long route you can start by getting several PCs and just start tearing them apart and learning what parts do what and what works with what and looking for answers to your questions on-line. Ask people you trust for help and do research at the library or your favorite bookstore, but…
If your looking to get into the field of computer repair (and get paid) and want to do it in the next 3-5 years, then enroll in a college, take classes in computer science and engineering. This will ensure that you get to learn what you need to learn in order to get a job where you will have exposure to all the varying types of problems that a computer has. So how long does it take to become good at computer repair?
It’s up to you!