How Long?
Actually the first answer is pretty complete.
I could add that reliable (not expensive necessarily} equipment helps,since you can spend your time flying with your instructor,rather than tuning and rebuilding.
Full size pilots sometimes have extra problems,since there is no direct connection to the plane,so no horizon to line up on ,and all control movement is reversed when the plane is flying toward you.Ego sometimes gets in the way too.....I think simulators help too,although I have never used one,but Im an instructor in our club and Im wary of the newbie,who tells me he can already fly,cause he learned on his simulator.I have seen one natural solo in two days,and I know of others who are still trying after a couple of years......Im guessing a couple of months is average but a lot depends on the time you spend at it.....