This is an interesting question to me because when I started I thought, I'll give it five years, and then at five years I thought, well, it will take another 5, and now I'm at 9 years and thinking, well, I need to keep going!! One "problem" is that I work full time and this involves travel. Another "problem" is that my idea of what "being good" is, is an ever increasing level of expertise. So, I'm just about playing things that students starting a music degree might be playing (which reflects the hours that I can put into it), but without the chance to go on to spend three years (or more) full time at Uni to really get over the various humps I'd like to get over, such as developing fluent sight reading, composition skills, and some deeper repertoire.
It's said that becoming an expert takes 10,000 hours. I worked out that university education for my profession was about that many hours (BSc, MSc, PhD, so not counting high school) and looking back now that was just the beginning of being an expert. So after 10,000 hours I was an expert in the tiny area of my PhD, and it's now expanded to be broader and deeper, some 20 years later.........
Progression doesn't feel linear, it feels like there are humps and bumps, sudden improvements and suddenly hidden abilities seem to "come on-line". In hindsight, it does get faster, bt at the time it always seems so slow
ah well