There are a few options that you have, but in my opinion the best is the Explorer Program that is commonly mentioned when it comes to under 18 year old junior firefighters. At one time I was an explorer myself. The biggest issue with starting a junior firefighter/cadet program is insurance. If you go talk to your local insurance company you will find that the cost far exceed the benefit of starting your own program. Local government bodies tend to shy away from them as well due to all the added risk. That is where the Explorer program comes in. The program is a branch of the Boy Scouts of America. There is a website here: http://exploring.learningforlife.org.../fire-service/ Go to your local BSA council office and ask them about the program. They will be glad to help you get one started. I think the cost are the same in every council. It cost $40 a year to register the Explorer Post itself and then $15 for each youth and adult that is in it. You are required to have so many adults. Adults will have to take a youth protection class which is offered online. Youth can be Male or Female from the ages of over 14 to under 21 and must have completed the eight grade. The Explorer program does some what limit what the explorers can do. However, the program does leave you ample room to teach your youth how to be a firefighter while keeping it entertaining. You are free to create your on training routine and structure.
The post that I was in as a youth was the first one in my area, within three years every other local department had one. Out of the 10 boys that I was in my Exploring post with 6 are still firefighters. The members of the hosting departments all got more active as they tending to start coming to the Explorer meetings as well as the regular dept training meetings. The youth will bring in a lot of energy that tends to infect everyone else. One word of warning though is to have a strong adult presence that can attend all the Explorer meetings. Sometimes that energy the youth bring will get out of hand. You will also have to watch out for the "Ambulance Chasers" that want to join you post. Keep a tight rope on those guys.
The post I am starting now will start with about 15 youth, but I am expecting it to grow to around 30. Your local BSA can help you recruit more youth to join. They will help you by setting up something similar to scout nights at your local schools where interested youth can come learn what your program has to offer.
I hope that I have helped you and Good Luck!