Beyond just the skills for the job, a General Contractor is also often self-employed, which means there's an entire other set of skills they must know, like marketing, interpersonal communication, and basic organization. If you can't constantly grow your business, then you'll be dead in the water. It's as much about getting the jobs as it is doing the jobs. It's not that those skills are impossible or hard to learn, so that's the good news. The bad news is that this isn't easy money.
I've known many contractors throughout my life and they are usually the guys who buy a house at an early age and do pretty well for themselves. They've got a four year head start on anyone going to college, and that's if you can get out of college in four years. Just remember that you may need to buy a truck and equipment, so what you save on school books you pay for somewhere else.