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.
"The future's uncertain, and The End is always near."
-Jim Morrison
Depends on how long you take to learn and how you define 'pretty skilled'
Main Gear:

ESP Eclipse CTM I
Dean 'Shards' Razorback
Chapman Guitars ML-1
Ibanez AEL40SE Acoustic
Blackstar HT-5 Mini Stack
EHX Metal Muff
EHX Small Clone
Depends on how motivated the player is to learn, and if they are a quick learner or not.
Castles made of sand
Fall to the sea
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
Quote by element4433
What if the way their wieners were positioned they could only pee into each other's mouths?

And one had his finger joined to the other's butthole?


Or don't. Yeah don't.