First of all, keep your age out of it. The longer you hold on to "I'm only 18" the more you limit yourself because of that fact. In fact, because you're only 18, you've grown up in the age of the internet and you have instant credibility.
Here's what I recommend. Forget focusing on web design or anything technical that you don't know how to do because then you'll just waste time trying to learn this new skill. There's other non-technical services you can provide that are worth a lot to local businesses but they don't even know how to begin.
Here's a few:
Google Places
Yahoo Local
Bing Local
Video Creation:
Animoto
Email Marketing:
Aweber
iContact
These are simple things that you can do without much technical know how but can make a world of difference to businesses.
The greatest mistake that offline consultants make is constantly looking for new money making strategies when they haven't even performed these simple services to get their first clients.
As you start making money then you can take the time to learn, outsource or develop more technical skills. For now though, don't go down the never ending "learning" blackhole.
Just go out, choose a friend or family members' business and do these things for them so you knock it out and get familiar with it once. Get a testimonial and then get clients right on Google (those businesses who are promoting using adwords but aren't in google places)
Hope this helps. I learned the hard way