The Japanese had all the Dutch imprisoned in Indonesia, not just soldiers. A number of male prisoners had been shipped off to Japan to work in labor camps.

Yes, but ancestor post says "He was a Dutch Soldier captured by the Japanese held as a prisoner of war."

At the end of the day, anyone who fought in the Boer war was born no later than the early 1880's.

If he was still in the military at that point, then wouldn’t that be an accurate description?

Of course. At that point though, it would be unusual enough [for a soldier to serve actively in 1902 and in 1945] that when interpreting conflicting points in a story, that you have to consider if perhaps the author hasn't gotten something mixed up in the memory or in the telling.

If I told a story about my own grandfather's service in World War II in the Seabees (by happenstance he was also a coal miner as a civilian), I'd be likely to get something wrong, not out of intention to mislead, but just that I pieced together the story in my own memories in a certain way when I was told the stories as a young boy. I may mix in details from my other grandfather's service or a great-grandfather's time.

Then, weigh that against a non-native speaker's chance to use a common English idiom "in the late 80s" in a non-standard way and against the chance that someone would express some negative interpretation of someone passing in their late 80s as being perhaps related to radiation exposure and black lung.

It's all speculation for all of us except one. ;)