It is difficult to learn how to read a music sheet alone. If you want to decipher this esoteric and beautiful language which is music you will have to be patient and thorough. You will also need to find a tutor to teach you how to read the music notes, especially if you want to learn to play a musical instrument. The time it will take you to learn to read music will vary according to the energy that you will invest in this task.
.Music is a language, some people learn it fast, others more slowly
It can take only a few months to learn the basics of sheet music deciphering. First, you will have to learn the clefs, the names of the musical notes and their associated sounds, the staffs, and the measure lines at least. It is a bit esoteric but not that difficult. Afterwards, you will have to learn the keys and the key signatures. In general, things are getting complicated from this stage. It is also quite difficult to understand quickly how meter and time work.
.Some instruments are easier than others, learn the basics with a simple instrument
It is easier to play the flute than playing the piano for instance. Some instruments require years of learning to master them. It takes at least a decade to be able to decipher most of the pieces of sheet music for pianos for instance. If you want to learn basic rules of music reading, you can begin with a "simple" instrument. We do not have a definition of what a simple instrument will be since it can be subjective and given that these are complex music scores for each instrument but let's say that you'd better begin with an instrument that you can manipulate easily. If you do not feel at ease with strings, do not begin with a violin for instance.
. If you want to learn fast weekly training is compulsory
As any language learning, weekly practice is essential if you want to progress rapidly. If you fail to practise at least once a week, you will probably feel stuck, and it might demoralise you. When you see little children playing highly complicated pieces of music on the Internet, you might think that it is easy to reach such a level in a couple of years. It is true for few people. Some people spend hours every day in front of their instrument but let's be realistic it is not something that everybody can afford.
.Music theory is complicated, do not expect to learn everything within a couple of years.
Music theory is complicated and it can take a lifetime to know everything. You will need to be passionate about music in order to learn everything. Brace yourself for a very long journey.
In short, if you want to learn to read music be aware that it is an endless journey. Musicians spend hours and hours each week deciphering pieces of music. Although the basics are quite easy to learn it takes years to learn how to play any piece of music properly. Playing a piece of music is not only deciphering musical notes it's also and above all rendering feelings of people that you will probably never meet. It does worth it to begin now and to keep learning up to the end of your life.