As a late starter, I'm unusually ambitious, although I suspect a fair few on this forum are the same.
I strongly believe I can acquire the required technical skill with time and dedication, but at the same time feel disheartened by the limitations of the quantity of repertoire that I may be capable of amassing.
I think, with perseverance and a teacher who clicks with you, you can achieve remarkable technical proficiency.
Time is the enemy, as others have noted. I think it was Yefim Bronfman who wrote that he had studied and learned the major concerti in the repertoire in his teenage years. Concertizing artists almost all have this head start on the rest of us. Most are voracious score readers who, very early on, do sweeping surveys of the repertoire and decide which pieces best fit their talent, hands and temperament. Then the process of winnowing the riches down to those pieces they play best begins. In the end, they are playing a modest slice of the repertoire at world class level.
What I have done, as an amateur with a degree in performance, is re-visit the heavy-duty works I learned as a teenager and young man. I never felt they were polished. So, that's what I am doing now and surprised and pleased to report that many of these works (Chopin "Etudes," Scherzi," Beethoven mid-period sonatas, etc.) are almost to a professional level. I think, with time, I could get them to a completely professional level.
But I can play many less difficult works at a professional level which is very gratifying.
In short, keep plugging away, analyze your technique for flaws, get a great teacher to help you fix the problems, and take a look at the big, ambitious works of your youth and re-work them.
I would assume almost all pro pianists routinely play the works they've grown comfortable with over the years (a MUCH larger repertoire than I would have, certainly). Newer additions to the repertoire are probably added one at a time, as a minority representation, surrounded by the tried and true warhorses.
Narrow your repertoire focus and take comfort in polishing the pieces you play best. Yes?