Tim,
I apologize.
I'm not going to quote your whole post because that would take up space. Perhaps you could answer some questions I have, though: How much of the decrease (Strictly talking the brain here. Psychology and Physiology are two different things.) in learning ability is caused by biological reasons, and how much by social reasons? How does the fact that the general population is not asked to learn a significant amount of information past high school or college affect the learning process at an increased age? Also, I did some light reading. The decrease in mental ability associated with age seems largely to concern the time taken to store information and to retrieve it. However, it was indicated that the integrity of the information once stored is not hampered. Is there more to this? Is this difference significant enough to prevent someone from learning a significant amount (like the skills to play a piece) after reaching age 50? How does the near-recent discovery that the brain does in fact replace brain cells affect this subject? I guess my bottom-line point is this: Is the decline in learning as a result of aging really worth the discouragement that older people experience when confronted with learning a new skill? You can PM me if you like, but I thought the answers that you know might be of use to the general population as well. Not to leave physical ability out, I've seen very old people play the piano spectacularly, and I've heard of older people doing such amazing things as running marathons (after years of inactivity). I'm assuming that there is hope, then, for those who would like to be "good" starting at an advanced age, physically, at least.
On the how many years subject, I gave you an answer: First, the term "good" was not defined and couldn't really be any more vague. Second, as you correctly assume, I am 30 years younger than you (when you went to Germany), at least. How in my almost twenty years of life could I have seen a number of pianists become "good" and thus give an estimate as to his figure? Unlike many, I do not feel comfortable teaching until I know much more than I need to. As I mentioned, going to college made a huge difference in my playing. However, this is in one year. I believe I am ready to work with beginners, but I will be doing so under the supervision of my professors, and I'm still afraid of making mistakes that I will have to "unteach" as I learn more. I've seen some of my colleagues teach, and, quite frankly, I don't approve of the hand positions they're ignoring, or of the fact that they have the kids sitting far too low. If they supposedly know more than me, and they make mistakes, who's to say I won't? I'm going to try my hardest not to, but I'm aware that teaching is completely different from playing. I'd like to be ambitious and say that any of those pieces you mentioned could be learned in one year, but if you have a child with small hands the hymns and the Joplin are out of the question if octaves cause stress. I can't truly be confident because I haven't seen other pianists go through the process. I've seen myself, and frankly I don't remember what it was like to be an eight-year-old pianist. The factors of dedication and time spent on practice (Dependent on work, school, and a host of other factors) and of what is done during practice also change the number.
For my personal definition of good, you should be able to play each individual part and any two-part combination of the hymn, as well as being able to voice each, well, voice, so your singers can learn the parts, or at least the soprano if for home performance. The Bach Inventions also demand voicing and a skill with trills that does not hamper the progression of the piece. I want to hear all the motives and I want to hear how they travel between the hands. In the Joplin I should hear the melody voiced, obviously, and after that I want the melodic portion of the bass but not the chords. The arpeggios should be even and the vast majority of the jumps in the left hand should be perfect (let's say less than five mistakes in the left hand). Everything should be performed at the tempo indicated, and all dynamics should be observed. That is good. You want better? Interpret. Good is pleasing to listen to, but interpretation and musicality make it interesting to listen to. Also recognize, as I'm sure you do, that you have asked for three completely different styles, and it is very possible to be good at one while being terrible at the other. I think you *may* be able to do that in a year if reading music is mastered within a month or two (meaning being able to find notes on the keyboard, being able to name them, knowing all the different markings, and learning to follow fingering indications).
And your skill level does matter. How can you give us figures without experiencing it first hand? Do me (or yourself) a favor: Get yourself a good teacher (if you haven't one already) and throw away all the knowledge of how aging affects learning (even if it's true and has all the data in the world to back it up). Take a stab at bettering yourself so that you don't have to "wisely refrain" from playing in church. I don't know how much time you have to practice, but even thirty minutes a day (If you're using some of bernhard's methods of practice organization) well-spent should make a significant improvement. Obviously, I wouldn't expect you to play like me (I'd be surprised if you did, because you don't sound like you have a lot of time to practice) as I practice about four hours a day, working several different pieces in the spirit of bernhard. But I would think you could attain my definition of "good" for hymns (if you haven't already) and that you could certainly come up with some dazzling preludes to share with the congregation. I tend to err on the optimism side, but it still seems realistic to me. Do this, and tell us how long it takes to better yourself.