One should wait until they are knowledgable enough about training and nutrition, and financially and emotionally mature enough, to get the most out of their cycle. Even then cycling is a whole new ballgame and learning how you respond and recover will be a whole new dimension to your knowledge. So while the first cycles can be some of the best, still it may take a few cycles and recoveries under your belt to really arrive, and avoid the yo-yo effect. So it really does not matter if you are at your genetic potential or not. If you have been plateaud for a period of years and your approach is solid, and you are committed enough, then you are ready. Actually AAS can be of great benefit to helping one achieve their potential. After roughly achieving ones potential then it becomes a matter of yo-yo'ing up and down above your potential trying to achieve a higher setpoint. Those that need to sport a physique beyond their genetic potential will likely end up being on more than they are off. Risk management then becomes critical if this is long-term harmful or not. Also when one gets older, since HPTA recovery may become more challenging, and hormone levels will not be as high anyway, people drift toward being on more or less fulltime, as HRT. At that point, hopefully this will enable them to operate well above their natural limit in regards to what would be natural for their age.
So for starters it does not really matter if you are at your limit or not. But if you cannot get to your limit and somewhat beyond with AAS then you are really in the wrong game. Once you go the AAS route, you need to think carefully about your long-term goals and what level it will take to keep you satisfied.