Summarize:

Take industrial arts courses in high school such as machining, drafting and woodworking. These types of classes will form the basic skill set you need. If you've been out of high school for several years, take classes at a local community college to brush up on your skills. Most of these programs take between six months and two years. A list of accredited schools can be found on the on the NRA website. Gunsmithing programs teach mechanical and tooling skills, the different functions and designs of various firearms, diagnosing and repairing guns, safety procedures, and in some cases chemistry and ballistics. Consider enrolling in an online gunsmithing program, a popular alternative in recent years. Gunsmithing programs always conduct background checks on their prospective students; those who don't pass are not admitted into the program. As an alternative or in addition to receiving a certification or diploma in gunsmithing, seek out a local gunsmith or apply through The Association of Gunsmiths and Related Trades (TAOGART) for apprenticeship status. In order to apply through TAOGART you must be 16 or older. All applicants must be able to legally own and possess a firearm in compliance to federal and state laws. If you are still in high school you must graduate and maintain at least a "C" average. You must have permission from your legal guardians and school officials (such as a principal or counselor). A gunsmithing apprenticeship consists of on-site training and classroom instruction that totals about 8,000 hours. This time can vary depending on the type of firearm apprenticeship you undertake. This license differs from other firearms licenses in that it allows you to maintain possession of another person's firearm for more than a day, as you would do if you were repairing it. In order to receive an FFL you must be over 21 years of age meet a number of strict gun safety requirements. A field agent will be dispatched to inspect your gunsmithing facilities and conduct an interview with you before the license is granted. Apply for an FFL through the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF). Check your local area for other licensing requirements.
Start early. Apply to a gunsmithing program at a college or trade school. Find an apprenticeship. Obtain a Federal Firearms License (FFL).