Its not how long you train natural. Its what you learn in that time. If you really learn things (training, nutrition and how YOUR body works (this takes lot more time than 3-4 years)) and get real results when you are building natural base, its going to be lot easier later. You don't have to use so much gear to make up mistakes and i think (after what i have seen) that you will do fine with really small amount of gear (like 250mg/wk of sust, 100mg/wk of deca and 15mg/d of dbol) even after first cycle. I don't believe that there is some natural growing limit in us, or atleast we can't never reach it. But i do believe that there is difference if you weight 170 pounds (witch is normal for many first time juicers) or +240 pound (not in contest condition, but not huge fatty either) before your first cycle (if you are midget 170 pounds is great of course, but i think you get the idea).