Umm, 10,000 ft is not really that high. I regularly hike up mountains above that with a t-shirt on and no extra oxygen, I only really have a problem with breathing at above 12,000 ft and that's at a brisk walk, not flying around on an awesome machine. So as long as he's not straining himself, even coming from sea level you won't run into problems with HACE or HAPE (http://en.wikipedia.org/wiki/High_altitude_cerebral_edema http://en.wikipedia.org/wiki/High_altitude_pulmonary_edema
) unless you're up there for an extended length of time. To be honest the biggest worry would be sunburn, you fry up there pretty easy.