My daughter was seven years old when she studied guzheng. When she was twelve years old (this year), she graduated from grade 10. Generally speaking, she only has one class a week, but you should learn how to play well at home. Generally, if you study hard in the sixth grade, you will pass Grade Two or Three in one year, and the later grades will be more difficult, so you can pass Grade One in one year. If you persist in this way, you can do it in about six years.