well, from personal experience I went from 90lbs to 120lbs after a year, 120 to 150lbs the second year, and 150 to 180 the third (also went from 5'7" to 5'11" in that time). I was a skinny kid (as if you can gather from my 90lb starting point. lol), and it's not like it was puberty weight, since I'd already sounded like a white barry white and was shaving once a week at 14.
arms weren't huge, but had good bicep peak and lateral head tricep separation (I did lack the long head mass I later developed), and my v-taper was there and my delts were already round and popping. so I knew how to make certain things grow and how to explain it to others. and I knew early on (from the time I was in the 3rd grade) that I wanted to be a professional bodybuilder (how's that for a pipe-dream eh?. haha), so i'd better learn how to do things RIGHT early, before I used steroids (which Id commited to doing early on).
bodybuilding, like any other endeavor, if you want to be successful at it, requires planning, goals, and ways to measure progress. I knew at the very least, if I never turned pro, or competed at all, i'd most likely still be making my living in the 'fitness' industry & training others. so I knew i'd better be a sponge early on, and absorb everything I could. lucky for me, I don't have a photographic memory, I have a "videographic-memory" and I remember EVERYTHING I read, hear, and see. So I can recall everything I learned about training, nutrition, chemistry, pharmacology, ect... and after a while you start to recognize contradictions in other ppl's theories and methods (HIT vs volume vs Milos vs Hany vs Duchaine vs Bachelodor vs Pat Arnold vs palumbo vs o'reagan vs trevor smith vs john brown vs ect... ect... ect... ) you realize they all work, but none work all the time. and you form your own theories and figure out what works for you, and learn when to change things up, and for how long, and to what extent, ect...
if you don't "think" about training, and why you're doing what you're doing, you'll have a very short bodybuilding 'career'. because eventually, with or without steroids, something is gonna stop working the way it used to.
I feel sorry (almost.. haha) for guys with supurb genetics, because everything works. look at flex, Ronnie, dex, to name a few pro's, but there are thousands of guys all over the country with similar genes.. everything they do works. try to have flex explain to an intermediate bber how to grow his stubborn arms, have Ronnie explain how to train chest, dex how to train back, mattarrazzo how to train calves, demayo how to train quads. they'll do a little of this and a little of that and 'poof!" muscle's grow! next week they do something else and 'poof!' muscles grow again... you think they understand why? or understand how to help somebody else grow? I doubt it, seriously. that's why they have trainers telling them what to do. lol.. what to eat.. what drugs to take, ect...
I think it's more important, at least equally important, (to building a natural base) for a guy to head to a thrift store and pick up some old copy's of endocrinology and pathology textbooks and try to understand how their body actually works before they use steroids, thyroid, insulin, growth hormone, anti aromatase, pde5s, anti-5a, or stimulants.