It depends on the person more than anything.
In my case for example, I had a friend, explaining the gear, lines, bodydrag, waterstart, etc., in 2 hours, and I took it from there all by my self.
Got a book, started to get really in to it. Have to say I learn more here on Kiteforum then anywhere else.
I know people, who take lessons two/three years in a row, and still have very little idea about the sport because for them its "only" for that vacation time once a year.
For me its part of my life, if not physically, mentally for sure...