I'm 6'4" and apart from having to do some heavy duty folding of the frame to fit into some light aircraft, no problem. No upper limit in aircraft manuals as far as I know, but some types can be a little uncomfortable to access for the taller person. Shouldn't be a problem if he's prepared to squeeze himself into the seat. Don't know of airline limits but have heard the military have a height limit for FJ to avoid leaving bits of the crew in the cockpit in case of ejection. Good luck...
