if you dont have a lifetime to learn, dont start cause you will never even scratch the surface in just a couple of decades.
seriously tho myself, i started as a child, tearing apart stuff... every mechanical present given to me was immediately disassembled to see how it worked.... then reassembled to see if it still worked.
my first gun was no different.... tore the deer rifle apart and cleaned it and reassembled before i even got out of my pajamas.... it was christmas day....
as i got older, i taught myself to refinish stocks.... this let me get my hands on old rifles from relatives... i refinished them and got to see how the different guns worked.... in the mean time i resurfaced a few sears on some old jc higgins single shot .22s that had been in the family for years but put away cause of the hair triggers as a result of 40 years of plinking....
eventually i got my hands on a copy of brownells catalog , "gunsmith kinks" and and the gun parts corp catalog (now numrich arms) .... i started cleaning handguns for friends , free of charge, just to have access to different styles and models....i advertised to buy non working guns....i fixed them and sold off the ones i didnt want.
eventually i took a course online... subscribed to a billion news letters and bought every tech manual and or tear down sheet i could find.
i got my ffl and opened my own shop in central california and made a nice chunk of change from my hobby till i got sick of the laws and requirements in california to do business.
this was all before the internet.... now anyone can figure out a basic repair. so if i was starting today, from scratch.... i would start here... and dont put a time limit on it, you are gonna run outa time before you run out of gun stuff to figure out.