Danny,
Welcome to the wonderful world of steam locomotive fans!!! I myself am 16 and live in Colorful Colorado. I have wanted to be a stem locomotive engineer all of my life, specifically on the Georgetown Loop Railroad here in CO. In fact, I am in contact with several people who work on the Loop. I would suggest getting in contact with someone on the railroad(s) you would like to work on, as they could give you a lot of inside information and tips. This is a good first step towards your goal. You do have to have a license to operate a boiler, but as for education,usually you need a good deal of mechanical experience and/or education can mostly be obtained by on-the-job training and experience. If you are interested in working in Colorado (by the way, where do you live?) there are three railroads that are the best in the state; The Georgetown Loop, Cumbres & Toltec, and the Durango & Silverton (you probably know this already). If you are interested in the Loop, here is there web address, and if you would like additional info, e-mail me and I can send you tons of info and photos.
The best of luck to you in your quest to obtain the best job in the world!
Shane Schabow