Mechanic

To begin with for A.S.E. (automotive) certification, on average you'll have two years of school with almost as much studying as a doctor to learn all the different designs and systems used by the various manufacturers and pass the certification tests for all areas of repair; engine, suspension, electronics & ignition, A/C system, A.B.S. sytems, etc... You will also have constant updates and re-certification tests for new models and system designs.
You will need to have attention to details and the ability to simply look at something and figure out how it works, know how to test it, and determine exactly what it takes to repair or replace it. You will need the ability to properly utilize various tools and improvise if and when specific tools are not available.
You need to be in shape to work in all sorts of positions in, around and under the car and have the hand strength to loosen and tighten nuts & bolts. You cannot be afraid of a few scratches or scraped knuckles.
Learn your MATH !!! You will need to be able to work with numbers including decimals, fractions and both standard & metric units of measurement as well for most all aspects of automotive repair, including electronics.
Being an automotive mechanic can be a very rewarding career if you like challenges and the sense of pride in doing the job right the first time as people's lives may depend on the quality of your workmanship. If you decide against this as a career, it also pays to learn as much about your car as you can so you do not have to pay someone else like me to do it for you. ;-)
Other fields like motorcycle & snowmobile repair are easier systems to learn and a good place to start. Aeronautical repair may have similar aspects, but require far more specific training and stringent qualifications.
You can take courses from institutions that specifically teach the different areas of mechanics, attend a community college, or work yourself up from a laborer position at a auto repair shop. However,