I think we use the term "genetic potential" to encompass a certain situation but in reality it is a misnomer. By adding AAS/slin, you are not doing anything on a gentic level, so you are still enhancing your body without finding a limit to that potential. Only when Anabolic Androgenic Steroids (AAS) & slin fail to produce for you would you be introducing hg/igf, at which you might conclude that your gentic potential had been reached. But, I digress......
Of course, we really mean how much you can grow without the introduction of AAS/gh/IGF/slin. I would imagine (just my thoughts...no numbers and/or proof) that less than 1% of the people who have ever used these substances did so upon reaching their natural limits (instead of genetic potential).
For each of us, the answer would be different. Applying a VERY broad brush to this one......saying that no matter what changes you make to your diet and supplementation (after consulting a sports nutritionist) and no matter what changes you make to your training regimen (after using multiple professional trainers with specific knowledge about the sport) you plateau and can achieve no more gains. At this point, I would think you have reached your natural limits.
I can't imagine what type of timeframe this would actually take given that most of us don't live this thing 24 hours a day for 7 days a week. Most of us have jobs and families which preclude such a situation in the short term. For the rest of us, this should really take many, many years.