How to Start a Home-Based Car Detailing Business (Home-Based Business Series) Paperback - August 7,2012 by Renny Doyle is a excellent book to read. I would also look out The U.S. Small Business Administrations website. The site will walk you through how to write a business plan. Writing a business plan is a lot of work but afterwards you will have a true sense of what you are doing, the market in which you are working in, and possible competition. Things to consider on the legal side is insurance, taxes, naming your business, and environmental concerns.
Do not listen to those that say your age is a problem. This is a great opportunity for you to grow as a person and make some money. Just remember that the publics expectations for having their car detailed is different then family or friends expectations.