How long are guitar lessons supposed to take before one can quit them and be pretty skilled on a guitar, on average?
Thats a real subjective thing, man. Different for everybody. I've never had a lesson Might teach sometime soon though.
Depends on how long you take to learn and how you define 'pretty skilled'
Depends on how motivated the player is to learn, and if they are a quick learner or not.
Like everyone else said its different for everyone, for me it took about 3 years until I was to the point that I didn't need a teacher anymore.
I'm 3 years self taught and pretty happy with my skills