Element #1 Hand-Eye Coordination
Much of the ease of picking up flintknapping has to do with good hand-eye coordination. Success comes to the knapper that can strike an area that he or she is aiming at. Failure and frustration plagues the knapper who failes to strike his or her chosen area as that is where breakage, hinges, stacks, and many other problems can originate. So I believe that there is a physical coordination base element involved.
Element #2 Practice, Practice, Practice..........and.......Practice
Over and over again, the quality possessed by knappers who have learned flintknapping quickly and progressed quickly, is that they would spend hours EVERY night and hours upon hours every weekend flintknapping. The more you knap the more your brain records and ingrains the methods and techniques. Something else happens too, you make mistakes and correspondingly learn how to fix them by trying new methods and discovering new tricks. Flintknappers like Woody Blackwell and Mike Santiago rose to excellent skill levels in just a few short years by investing huge quantities of time practicing. Most knappers probably do not knap every day. I knapped many days per week in the beginning, but knap once or twice a week now. You will go through huge amounts of raw material practicing, therefore I recommend using renewable lithic sources like toilet tank lids (Jonstone) and glass bottoms of jars to supplement your good rock supply. I still have some points made from Jonstone that were created in my first couple of years of flintknapping.
Element #3 Artistic Abilities
Some may argue with me on this element, but I've watched flintknappers who have been knapping for a decade or more and their points just never progress beyond a simple tool look or field grade look. There is absolutely nothing wrong with that, as those flinknappers have simply reached the ceiling of their elements and are quite content and happy staying at their particular skill level. I've also taught a few beginners and noticed that those who already do other artistic things like painting, drawing, writing, wood carving, sculpting, etc. seem to have an eye for balance, shape, and flake scar patterns that help them progress faster than those that do not have the artistic inclination.
I do not believe this artistic ability affects how a knapper flakes his stone, but will affect how a knapper chooses to take off strategic flakes from his or her biface. A nonartistic eye would remove flakes out of necessity in order to shape a tool for function, while the artistic eye shapes the biface for function as well as eye pleasing form (e.g. opposing flake scar patterns, symetry, typology correctness). The more artistic you are, I believe, the more likely you will be to progress to the tops of the flintknapping art. The only exception to this that I've observed so far seems to be those individuals that are excellent carpenters and machinists. Those talents, for an unknown reason, also lend well to developing good knapping skills. Perhaps it's that excellent carpenters and such connect with that same right brain ability as artists. I'm no psychologist or doctor, so I'm just taking a wild guess on that one.
Element #4 Availability of Raw Materials
When a knapper lives close to a source of good chert, he or she has an almost unlimited supply of stone to practice knapping with. So this element ties in with element #2 in the aspect that the high availablility of raw materials allows the new knapper to be able to afford to practice more with good materials. When I was in my first couple of years of knapping, I couldn't afford to buy a lot of stone, so this forced me to knap less and to be more cautious in how I knapped so as to avoid as much waste through breakage as possible. While this small quantity of raw materials allowed me to develop an early respect for stone, I also believe it slowed my progress. The first year I could afford to buy a bucket or two of good rock, was the year that really helped me progress by leaps and bounds.
Knappers have a saying "Make it or Break it", and what is meant by this is that if you are afraid of breaking the stone, it will impede your ability to complete the point you intended to knap, so go for it even if you break it.. Having access to a source of Esopus, I've progressed quickly in learning how to knap it as it was of minimal cost to me. I do still hate to waste good stone, so even when I break bifaces of "free" rock, It still bothers me, I just think I get over folding the piece a lot quicker knowing it only cost me my time to go get it.
Element #5 Access to Other Flintknappers
If you can knap regularly with experienced knappers, you will be able to watch them knap and be able to ask their advice when problems arise with your own knapping project of the day. Watching an experienced knapper reduce raw material to finished points is one of the best ways for beginners to learn the techniques of flintknapping. I unfortunately did not live close enough to any experienced knappers to take advantage of their regular teaching when I was a beginner. Some of this was a lack of knowing local knappers. I was able to eventually learn much form the likes of Jim Redfearn, D.C. Waldorf, and Craig Ratzat. In fact, I used to get lessons from them any day I wanted because I bought their video tapes. For the new knapper who lacks access to experienced knappers, videos can be a great substitute. As you watch and rewatch these videos, you will see something new each time. As you progress in your skills, you will find that you can refer back to these tapes to watch for specific skills that you are looking to master (e.g. billet selection, striking angles, and platform prepartion)
Now that all that is out of the way, let me see if I can tie it all together and actually answer this question. It has been my observation that master knappers have high degrees of all five elements and tend to have learned very quickly. Knappers below the skill level of the masters may progress to be masters some day, but will have strong elements and weak elements that make-up their skills until then. For example, knapper "A" may have high elements 1,3, and 4, but low elements 2 and 5. Knapper "A" would likely fall into the intermediate level of knapping ability. If knapper "A" makes more time available to knap (element 2) and attends a few knap-ins (element 5), his or her skill level will likely rise along with the quality of his or her knapped products. If the knapper posesses all the elements it may take as little as 3-6 months to knap an acceptable replica of an arrowhead. However, a knapper with fewer of the elements may take up to a year before he or she is able to knap an acceptable arrowhead replica.