This is a very good question. Every beginner I know, whether they are 6 or 66 years old, want to know how long it’ll take before they are able to play what they want to play on the piano.
If I give a cookie cutter answer, I’d say that with a little practice and a steady dedication, within three months the student should be able to doodle a little song, right hand playing the melody while the left hand knits a simple bass arrangement.
Of course, not every one is built the same. But I usually have people playing a simple song by the end of the first lesson. Something with both hands playing the same notes. It is not that easy, by the way, since the lowest note on the right hand will be done by the thumb and the equivalent on the left hand is played by the pinkie. I hope you are able to follow and I am not getting too technical. If you are lost, I know an excellent teacher in Mayfair neighborhood who can explain in clear and easy terms what I mean.
The question, how long does it take to learn the piano ask another question: What do you want to learn? Yes, you will have to make a choice. Actually “choices”, with an “S”. Piano covers the whole range of style, eras, orchestration, etc. From Bach to Elton John, from Chopin to New Orleans. That’s because piano, or keyboard, has been at the center of music since the 16th century, and also the instrument that covers all other instruments. For example, piano, besides having a massive literature dedicated to just piano sonatas, concertos and the like, also has an enormous library for symphonies, operas, pop songs, transcribed just for the piano. You can find easily those books of the complete Beatles repertoire for example written for piano. Yes, that’s what I’m talking about.
But, if you think this is complicated, consider this: Some people want to study improvisation.
Jazz? Blues? Boogie Woogie? Classical? Will it be in the style of baroque? Will it follow the chord progression of the Canon of Pachelbel? Will it be based on a walking bass line? The number of possible routes are innumerable and confusing.
Fortunately, with a few pointed questions, the beginner student can be put on his path and start the journey of learning what he wants. It takes an attentive teacher. And, it just so happen that I know one that can guide you. He doesn’t live far, you should look up what people say about him, etc…