I agree about trying to fulfil our full potential. For me personally, in my mid fifties, I find that setting aside enough time to practise is difficult with work committments, but I do make the time. Also, trying to maximise the efficiency of practice is crucial as well. For example, not wasting time just playing the same difficult passage over and over, tripping up at same places, physically or mentally or both; rather, drilling down to the problem, identifying it, then working hard to fix it through very focussed and intensive practice. This sometimes involves adjusting the fingerings as well as slow practice, gradually building up to the required speed and then placing back into the whole context of the passage or movement. This approach is nothing new of course, but I am very rigid with it given the limited time I can find to practise properly.
In terms of declining, I think a large part of it is to do with memory as well as physical. I still find I can play the same physically demanding music I did thirty and forty years ago (long may my stamina last, hopefully, I do try to keep fit generally), but it is my memory that I feel is declining a little. I just wonder what we can do to sharpen this up, particularly in longer pieces. For example, I have nearly completed learning Chopin's Fantasie in F minor Op.49, but am finding memorising difficult at this stage, the same themes coming back in two or three different keys with many accidentals and consequent fingering adjustments. I am nowhere near ready to perform this publicly yet. Any thoughts from anyone regarding maintaining or even improving memory in a specifically musical context?
I remember watching an ageing Sydney Harrison performing as part of a Beethoven masterclass, and he had a memory lapse towards the end of the finale of Op.13, forgetting the changes that take you into the coda, instead ending the theme as previously on a perfect cadence. I could really empathise with that, and I was only 17. Sydney was a great teacher and performer, but I can't help but think his memory was sadly beginning to go. He used to teach my teacher who was also taught by Fanny Waterman. I remember discussing this memory lapse with my teacher, and she said, these things happen, largely due to nerves, the equivalent of actors occasionally forgetting their lines. Which opens up another can of worms for discussion, how to control performance nerves! Does the ability to control nerves decline with age too? For example, in later years, Richter was famous for cancelling concerts due to nerves.