Even only just being past a half-century, I've run into this situation a few times.
Part of which comes from an after-the-fact familial observation. If I talk about my grandfather, on of the things that will crop up is that he was a MoMM/1 on an AK at Anzio. One of his stories was of how they rotated the snipes on deck after long stretches of GQ stations. While on deck, the gun line was supporting the landings. The 14" shells he saw were from USS Texas.
This is often where I "lose" listeners whose grandparents' service was in VN; that I had a grandparent in WWII boggles them. That I attended a family thanksgiving where the "adults' table" where, of the 16 present, only three had no military service (the 2 WAC, the Wave, & the Wasp skewing the demographic a bit).
Every so often, I, too, fall prey to this--when I consider my family tree contemporary to my Great-grandfather, who was called up for service at a naval base for the Spanish-American war. Which is more than a century ago. To add to that, my paternal GGF's younger sister had 13 children spanning 26 years. Her youngest child is scarcely older than my own father--which can boggle.