I have spent the past three years (almost four) working with a master builder and fabricator and will keep working with him until he decides to pack it in... at 80 my mentor is still feeling inspired and now we are working jointly on some projects and independently on others. After a year of working together (part time) he said I was ready to start flying solo as he could not teach me much more.
Not too many people have that kind of opportunity... most of our work is filet brazing and most of the work is done freehand.
I came into this with a background in fabrication, a lifetime of working on and studying bicycles (geometry does not confuse me), and using the torch came pretty naturally as I have also done plumbing work.
I get to use the torch a great deal as even if I am not building frames I am doing repairs, custom work, and building custom racks... this is what helps pay the bills as the number of people who are willing and able to purchase a custom frame are a very small percentage of the market.
I see quite a few amateurs building very nice looking and competent frames... and this is what frame builders used to do when it was a more common trade and not a boutique affair.
Ron Cooper was one of my heroes and he built some truly beautiful bicycles and said he never felt he could put his own name on a bicycle until he had done this work for 20 years... he apprenticed under the master builders at A.S. Gillott and then became one of their primary frame builders.
He was building a frame a day for most of his adult life.