Chopin composed “Fantaisie” when he was 24. Difficulty is level 9, advanced, just before master level. My guess is that two hours of practice each day from now on will be required for Robert to progress.
Another guess is that when he enters his late teens, he will gain some independence from parents and piano tutor and be able to put more of himself, and no one else, into the music.
If I were his tutor, I would be waiting for that moment, which will happen if Robert continues, and that will be the moment of real graduation.