A little putting around in the weeds on a dirt bike does not qualify one to ride a heavyweight bike on the street, no matter how big he is. I strongly suggest a riding course first, preferably starting with a midsize bike until he learns how to maneuver the bike comfortably in all street situations, including panic situations. There is a big difference between just learning how to operate the clutch, shifter, and brakes, and actually learning how to ride safely on the street. Do him and anyone planning to ride with him a big favor and strongly stress the riding course.
Once he is "qualified", someone his size shouldn't need to start small like most of us old timers did. I agree with earlier comments, do the test ride thing at some dealers or rent various bikes to see what he is most comfortable with, then buy what he wants.
Jerry