Like Tanzie, I was told a lesson for every year of your life. It took me around about that but I did get practice with my parents in between, not sure if that was always a help...
When I took my motorbike test it took me around 15 lessons but I was nearly 30.
Dh rode a motorbike from being 8 but didn't start learning to drive a car until he was 33. He booked a stack of lessons with BSM all within a week but not an 'intensive' course, so he did around 2-3 hours a day and passed his test the following week.
Obviously he had already had road sense and I took him out prior to that to sort out clutch control etc as almost everything you use your feet for on a bike you do with your hands in a car & vice versa.
I think it depends how practical you are, and how quickly you learn new sequences of actions without concentrating on them; you need to know that if soemthing went badly wrong you would instinctively react well.
I might be in a minority of 1 here but do believe that being allowed to drive is not a 'right' and there are people in the world that really shouldn't be allowed out in a car - we have a saying in our family
'did you find your licence free in a Cornflakes packet'.
It shouldn't be funny to joke about being unable to park for example.
To get back to the point, I think it depends how practical you are, and how quickly you learn new sequences of events without concentrating on them; you need to know that if something went badly wrong you would instinctively react as best you could.