Having gone through this with my two sons in the past 12 months, I can tell you how my boys, 17 and 15 years old, did it. They both started out a few days before Thanksgiving 2019:

- they both took private lesson twice a week, each lesson was an hour;

- they practice an hour in the morning before school starts and 2 hours after school, on weekdays,

- they practice 5 hours on both Saturday and Sunday.

Why did they want to do this? For them, dating pretty girls is the primary factor, and it is already paying handsome dividend for them. As a father, I am very happy that they pick up a new instrument, in addition to the piano. Something they can enjoy for the rest of their lives.

My advice to you is to have a goal to motivate you to practice harder everyday. That will speed up your improvement very quickly, and have the discipline to stick with it.

Best of luck to you.

P.S. they are only taking guitar lessons once a week and practice 90 minutes everyday for the past two months.

Here are some of their recordings after eight months playing guitar: https://soundcloud.com/john-mayer-138996963