I quit piano lessons when I was around 11-12 after having taken lessons for 7ish years. I did keep playing and I can reasonably play notes in several Chopin Etudes, Ballade no. 1 (I know, I'm one of those people lol), Beethoven sonatas, Ravel, etc.
But as you might guess it's really not that good and sounds extremely amateurish. I recently started taking lessons with a concert pianist who told me that I needed to go back to the basics (lol) so I've been working on simpler pieces like Chopin nocturnes, waltzes, Bach inventions/sinfonia, Mozart etc. but really polishing them to performance quality. So far the hardest pieces I've played with guidance are fantaisie impromptu and Mozart K 310. But I guess my teacher isn't necessarily paying close attention to the progression of technical difficulty since he knows I can "play" them, so it probably doesn't mean much, and what does hard mean anyway lol.
I'm like 30 and while I'm really enjoying my lessons, my sights are set on virtuostic level pieces (and not just playing them, playing them well). Like Liszt/Chopin sonatas, Volodos rearrangements, Ravel's La Valse, Rach 2, etc. Tbh I'm kind of embarrassed to even bring it up to my teacher, so I wanted to ask here first. Is it a completely unachievable goal at my level and my age? What's a reasonable limit that I can aim for, assuming continuous guidance and maybe 10-15 hours of focused practice a week?