He is playing tennis and used to ski. He knows how snow works, how edges work, how to read terrain. Ime tennis is hell on my 53 yr old knees...stop go, twist....ehhh boarding no problem. I think with excellent instruction, going over how to fall, the mechanics of getting back up, good body posture and how to turn. No problem...just predose with ibuprohen to help prevent the swelling before it happens.
edit: Get your old pops a day long private lesson with a hot chick snowboard instructor (motivation and gender pressure so he won't puss out) and buy the beer at the end of the day.