Timaeus

Been weightlifting for a while, with very good results, but biceps still lack a distinct "peak". Is this a genetic limitation? Body fat currently at 10% and arms measure 16inches flexed. Any advice?

I recently participated in the so called "300" workout and was able to complete the workout in 22 minutes and then began the workout again and worked my way to a total of 500 repetitions overall. Would this be a good indicator of one's overall physical fitness? Are there other criteria used by trainers, dieticians and strength coaches? What might be some specifics in regards to those criteria?

I have been strength training for several years and achieved good results. I am still able to make gains in strength and endurance, work to push past plateaus, follow proper nutrition, and recommendations for rest. However, the development of my muscles seems to be at a set point. For example, the girth of my upper arms (flexed) is at 16 inches (cold) 16 and half inches (after exercise). My ratio of lean muscle to fat (BMI) remains fairly consistent (9-10% body fat) This has been the case for a few years. Does this represent a genetic limitation in the human ability to naturally develop muscle? Would a 16 inch arm represent the upper limit of muscular development for an average male? Should I simply remain content with my progress or can I work towards something more? Any insights or recommendations?