Conduct an oral history. Get a tape recorder, ask him a couple open-ended questions, and let him just talk.

Ask him about people who were important to him, then why. Ask him about places that meant something to him, and why. Ask him about events in his life that were important, then who was there, and why it was important. Ask him about how these things, events, people, impacted his life later on.

Ask him about the things that made him who he is today.

StoryCorps has some tips for interviewing, they also have an app that you might be interested in.

It's worth getting some genealogical info. Even just general, who his relatives were, the earliest ancestors he knows of, their jobs, where they live etc.

Even if you're not interested in it yourself, a lot of information may exist solely in his head, and if not recorded will be lost for anyone else whose interested in his ancestry.

In 200 years, he will probably have hundreds or thousands of descendants, many of whom may be interested in their ancestry.

Ask him if he'd like to participate and be open to the possibility that he may have other plans for his final days.

Find popular songs from different periods of his life... Helps to jog the memory