I need to take a step back and start building up a good range of repertoire in a variety of styles starting from the easier levels, otherwise I'm always going to be struggling with a very small number of advanced pieces that take me ages to learn and are never fully mastered anyway
I forgot to mention one idea -- that you won't like I think. There are essentially two approaches to acquiring piano ability. In one, students progressively pursue graded repertoire
(including etudes) to the almost exclusion of dedicated and systematic mechanical training
. In the other, repertoire is added to a systematic and exhaustive course of mechanical training
. This second approach is famously the "Russian School" approach, and is discussed very succinctly by Joseph Lhevinne in his little book Basic Principles in Pianoforte Playing
, wherein he states that at the Moscow conservatory, the student would not even be allowed to present their repertoire for evaluation until and unless they had first passed their technical evaluations! Admittedly, this refers to the serious
business of learning the piano, but the principle is clear. In the first, the preparation is very narrow and has little transferability. In the second, the preparation is foundational and is easily transfered to any repertoire. How much of the second approach you would be able or willing to pursue, and what hope of achievment as limited by your age, is somethng that only you can answer for yourself. Just something else to think about.