Exactly, I would expect this person to perhaps have some additional mutations (in his superficial tissues so no body wide mutation of course) due to radiation,

Exactly, I would expect this person to perhaps have some additional mutations (in his superficial tissues so no body wide mutation of course) due to radiation, or perhaps due to selective pressures working differently on them in 0 G. Also I'd expect expression changes (RNA quantity changes), also related to 0 G or maybe to his diet. Also, it is often claimed that chimp DNA is only 1% different from ours. Which is also bull of course, it depends, (as here) on how difference is defined. The telomere story is interesting but from the text it sounds like we already expect that from radiation and calorie restriction.