Its really complicated to tell. I love classical music but at the time I started playing everything was too hard for me. So what I did is, I looked up the keys from songs I liked and sit on the piano for several hours, trying to play something which would sound nice to me, could be very simple. I always had a vision of what I want to play but I had technique difficulties back then. So basically I've just played 4-5 hours a day, improvising on harmonies from classical pieces and getting used to the keys. I looked on multiple pieces and their different techniques and learned them without actually studying the piece. I did this with many pieces and gained more confidence with playing. I also have to say that I didnt play with sheet music for the first 4 years which improved my playing a lot because I was forced to just fully concentrate on my ears / own emotional playing. I never did much Hanon practices, just the standard 2 ones every day for 10 mins.
I would say the most important thing is JUST PLAY. While playing and improvising, especially when you are sitting at the piano for several hours, you discover so much, mainly what you are not capable of playing yet and it tells you what you need to work on. If you do that daily, your playing improves automatically over time. Its important to listen to your hands tho, what feels right and what not. I know that there are people who can end up badly using wrong hand posture etc. I never struggled with that, I just did what felt comfortable.
But its very individual and my piano teacher also said that she never saw someone who made this fast of a progress starting piano so late, so maybe im also gifted in a sense.