There's so much to not just read out of a book, but just the tools and equipment needed to become a smithy is very pricey, so you being so young is to your advantage.
You need to first know how metal parts is made. This is where being a machinist comes in with lathe, mills, manual crank & electric hand drills all way up to drill press, routers, Dremels and their tool accessories, saws(wood & metal) and even the lowly hammer and nail.
Hope you have a steady hand when it comes to taking a block of wood that could cost upwards of $500 due to its character, then using powdered sander(s) and your own hands to shape that wood into a rough form, then take wood carving, other(different) woods for forearm tip and heel along with epoxy and join up, make a comb and then checkering the wood and finally doing a TruOil or French Handrub finish, to turn that what is already expensive wood into a $1500 gun stock
You'll also need to learn metallergy. This is knowing your metals and what's needed for making or repairing a part with welding, silver soldering, heat treating(if needed), then also learning about the different forms of "Blueing" from cold to hot acid(salt) dipped for whole guns or just sanding/polishing/buffing then metal treatment for spot blending after a repair.
Nowadays there's the ceracoats, duracoats and other metal treatments and coatings.
Gunsmithing is a beautiful hobby that takes days to read about, but a lifetime of being an apprentice at, since there's so much to learn.
My dad was a "country" self-taught gunsmith. He had 30+ years of working as a machinist. Helped neighbors or the family with their gun mishaps. He made much of what he needed, such as bluing salt tanks, some carving/checkering tools, carved and shaped blank stocks to fit actions/barrels for hunting rifles he built. What I mean by built, he would purchase old Springfield 1903 30-06 mauser action rifles or abused Remington 700's and completely disassemble them down to the last nut and screw, cut the barrel if needed, then sand, polish, blue(or nickel finish) all needed parts and re-assemble until he had a finished product. I helped when I could and learned much from him. He had books -- man did he have books about everything that involved a gun from screw sizes and taps needed, bullet types from weight to length, to barrel types/bore diameters and best barrel twist(s) for type of bullet used.
A gunsmith's life is always learning about not just the old stuff, but also what's new and shiny that comes along.
Good luck Mr. Borax, you have a great life ahead of you if you continue into this much needed field. I have the talent to do my own gun fix and repairs today, but my age is against me to think about doing gunsmithing as a job.