Just to make you doubt yourself a little more... My vote is to go and try to achieve what you WANT to do, not second guess your intentions and abilities based on other people's fear.
If you're young and motivated, I say try and make it your own way. Odds are if your parents are willing to help you out now, they'll still be willing to help you out a year or two from now if you cant make a go of the mechanic thing. (In my experience, parents are even MORE willing to help if you come crawling back and admit that they were 'right' about something 
You can ALWAYS go back to college later in life. Theres two schools of thought, obviously...
My brother started sweeping floors in a machine shop, and a few years later he's ready to write his final machinist exam. He took a few months off, here and there, to get the schooling he needed just to get papers. But in the meantime he was learning hands-on in the field that he enjoys. I had a friend who spent two years of full-time college instruction to get to the exact same papers, and then a few years of apprenticeship, and now he's unemployed.
...
People are most often motivated out of fear. Fear of regret is the biggest motivator of "life changes." Most of us stay in jobs because there is no HOPE of more money for less stress. We fear that we'll regret leaving the job and making our lives even worse. So we stay where we are because we aren't willing to risk what we've already got, which tends to be less than we wanted anyway. Sure its a risk, but the rewards of BELIEVING IN YOURSELF can be much greater.
The fact is, you're young and you've got nothing holding you back right now. Spending a few more years in school is an option, but is that going to bore the pants off you while you learn stuff you'll never use in the real world?
I love the guys on this board and they obviously speak from experience. BUT ... determination and INTENT is what will move a mountain, not the guy standing back saying "you better not try cause the odds are against you"
If you're avoiding school because its hard work and you're feeling lazy, take that into consideration. If you're avoiding school cause you have a drive to be something and school will hold you back, take that into consideration too. Go with the motivation thats POSITIVE, not based on fear.
Its obviously not going to be black and white... but in the end, I think a happy life is usually NOT the one where you made the most money, its the one where you fullfilled your potential.
If all else fails, DO BOTH. I'm sure you can get a job doing menial shop labour part time whlie you take that business degree or whatever you decide to 'learn.'
Thats my two cents, still being a computer programmer who wishes to be baking in a sand cubicle under the hot mexican sun and a superbeetle.
-biggie