Well, Norvig really means _mastering_ the thing. For him, this includes learning half a dozen languages, learning them well, applying them in all kinds of projects with others and so on. This probably can't be done in two years.
I think, with the right resources (people, material), if someone dedicated themselves to learning programming/software development actively for 2 years they could become extremely proficient in it. Not masters across a number of different languages and paradigms, of course, but just very proficient in a few of them to the point where they could churn out good work/projects/ideas with it.