My book groups have been together long enough to show some consistency. They also are very different groups with different people attending.
The Monday night CS Lewis group is in its 5th week reading "The Weight of Glory." The CS Lewis group is an older crowd than the Tuesday Night Dead Poets Society. In fact this week's CSL group was five people: three Army, two Air Force. Four men, one woman. And by rank, two captains and three lieutenant colonels.
Tuesday night was the intro to Aeneid by Virgil. That meeting was a dozen soldiers and airmen with three officers and nine enlisted. Most of the enlisted are in their 20s. There are a two sergeants in their 30s. So the 800-year-old and 2100-year-old books attract the young people and the older people read CSL.
Five of the soldiers go to both groups, but the only person never to miss a meeting is one of the chaplains in our brigade. He also asks the best questions and makes some very good comments. For instance, when we read CSL's "Why I am not a Pacifist" he brought up the people in dictatorships who have no option but passive resistance. It was outside the scope of CSL's essay, but an important way to look at non-violent resistance.
It's two hours of very good conversation every week.