I think everyone is capable of hitting great golf shots more often than they would realize. Of course everyone's good shots are good. If a 20 handicapper happens to hit it to 2 feet on a par 3, its just as good a shot as if Ben Hogan hit the same shot to 2 feet. The difference between low handicappers/pros and amateurs is that the better players hit bad shots less often. Their misses are just better, plain and simple. So I think any student is capable of building a repeatable golf swing that can produce consistent shot dispersions and results.
As far as things holding someone back, first I think age is a huge consideration. Most older people I teach are so caught up in distance, like everyone else that plays golf. However, people need to understand that a 60 year old can't outrun a 20 year old, can't out lift him, can't do many of the physical things as well. The unfortunate truth is that as you get older, you just aren't going to hit it as far as a younger person is capable of. Also, injuries, physical disabilities, and other like issues can cause a person's swing to produce less distance, as well as less consistency. If a person is in good physical condition, that person is capable of a repeating swing, with a repeating trajectory. He may not blast it 320 off the tee, but hey, look at Zach Johnson. He averaged around 265 off the tee at Augusta, and Mickleson lead the field in distance once again at around 302 average. Who's shoes would you rather be in?
I think that if a student is dedicated to getting better, the sky is the limit. Obviously tour players have a little something that most everyone, even very good players, don't have. So I am not saying that I could take a 45 year old accountant with a 17 handicap and put him on the senior tour when he turns 50. But, I could take that 45 year old accountant and make him a very competitive player for his age group, and make him enjoy the game like never before.
Hope that answers your question, thanks for your participation in the forum.