I can't imagine even the North Koreans being too hard on him physically given his age.
But chances are they will go after him from a mental perspective... and try to get him to admit to war crimes of some nature, this will be to the benefit of the regime if he does so.
What did he do that was stupid?
Enter North Korea.
Again as Dem said this is incredibly rare especially for a tour group, I almost did it myself, my fascination with North Korea even amazes me sometimes but in his particular case... he is a Korea War Veteran and what he did was incredibly risky by entering the country.