The question is asked by students and parents alike. When I first started out as a teacher, I would respond with phrases like, "it depends on how much time you dedicate to practicing" or, "about six months to a year or two" to give them a benchmark of basic ability. It takes an average of at least 7-10+ years of dedicated study to have a sense of self mastery of the instrument. The amount of time is vague at best and it depends on many factors like the number of hours of dedicated practice, the student's motivation to play, the quality of instrument they have (whether it's easy or hard to play), and the learning pace for that individual.
The classical guitar is one of the most beautiful instruments to play yet requires a focused dedication to master. Results can take longer to appear for classical guitarists than say for someone who wants to play songs by Billie Eilish or AC/DC. As fun as those songs can be to play, they don't necessarily activate the artistry within your soul like the classical guitar does.
Parents may wonder why their child (A), who is learning the classical guitar, doesn't sound as polished as their child (B), who is learning the piano, even though they both have been playing their respective instruments for the same amount of time. The piano analogy is helpful to understand. A student studying the piano for two years will undoubtedly be able to play more pieces than a classical guitarist who has played for the same amount of time. The quality of sound and the speed at which the pianist can play will often be more developed than that of the guitarist because the learning curve to produce a good sound on the piano is lower than that of the classical guitarist. In the early years, the placement and motion of the fingers for the pianist do not need to be as intricate compared to the guitarist. For this reason, it takes an average of two years (maybe more) for the guitarist to produce a nice tone. This is not to undermine the difficulty of playing the piano by any means. During my conservatory days, it was the piano students who were first to sign up for a practice room for the week because their repertoire was the most demanding. Pianists have their own challenges to address, such as having to worry about ten fingers instead of a guitarist’s eight as well as their feet on the pedals. Conservatory players are at the highest level, however. To put it plainly, a young child who hasn't had any piano lessons, could press a few keys and we might be able to distinguish a nice melody. Whereas, if they were to do the same thing on the guitar, we would hear violent clanging and the buzz of open or muted strings. Again, at the very basic level, it would seem that the pianist sounds "better" than the guitarist, even though they both have been playing for the same period of time.
Once the left-hand fingertips are strong enough to accurately press the strings down behind the frets, and without blocking the other strings from ringing clearly, the other 80% of the sound relies on the placement of the right hand, quality of finger stroke, and the strength, texture, and contour of the nails (if the student is playing with nails). The precision, synchronicity of both hands, and knowledge of the abstract tuning of the strings requires a large amount of motor skills and cognitive ability to play the classical guitar reasonably well. I have had students who played rock/blues guitar for years before coming to me for classical lessons and when asked to play a basic, single-line classical guitar exercise with their fingers, you would think that they picked up the instrument for the first time. This is why the classical guitar has among the steepest learning curves of any instrument and therefore requires the maximum amount of time to develop before the student produces any noticeable results.
I tried teaching myself the guitar in high school using the internet and learned my favorite songs by looking up guitar tabs. It wasn't until my second semester of college that I began studying the classical guitar from my college professor. Like most 18-year olds who are into rock, I was content with just playing power chords and the pentatonic scale. Lessons were challenging at first and thought to myself at the time, "I've been playing the guitar for 4 years. Why is this so hard?" It was as if I had been making grilled-cheese sandwiches and suddenly I was learning the ways of French cooking. I continued taking lessons as it was part of my music-business major while continuing to play pop, rock, and reggae with my friends in a band. I don't know when the shift occurred, but it likely happened 5 years later for me. I was working as a cashier at a local grocery store and during my day off I decided to go to my college's music building to grab a practice room at 4:00pm. I brought with me a 2-pound bag of cashews from the bulk section of the store where I worked and stayed at the music building until midnight practicing fundamental classical guitar exercises along with a couple of pieces that I was currently learning. Suddenly it clicked for me. Around the 6th hour of practicing, the world was put on pause and it was just me and my guitar. I can't describe to you the intimacy I felt with the instrument and how powerful that was for me at the time to feel so focused and connected to pursuing an art like the classical guitar. I remember watching a movie years ago called "4 Minute Mile," which talks about the point at which everything clicks and you feel like you can do anything. The classical guitar, as challenging as it can be, has the power of showing that you can achieve something you might not have otherwise thought possible.
Like in the story of the ugly duckling, if you allow yourself the time, you will be rewarded with being able to play one of the most soul-achingly beautiful instruments that exists, flying high as the swan you were meant to become and sore into the hearts of those around you as well as your own. The world-renowned classical guitarist David Russell has said, “the guitar sits right up against the heart. It is no wonder that it is beloved by so many, especially to the player who plays it."