I often find it a bit hard to picture Vaughn, who is well over a century old, doing action scenes like he did in Battle of Betazed, regardless of advances in medical tech. Did he, in his intelligence work, encounter an alien that slowed his aging process or something? On the cover of Avatar, he looks like he's in his late 50s...compared to how McCoy looked at 137 ... he looked ancient.
You've never met an especially fit older person? I've run into a few. There are some people who look younger at 70 than others look at 50, and who are more physically fit and capable than others are at 40. It just depends on the person.
Physically fit... yes ... able to get into fisticuffs at 100+ years old ... no. (Didn't he fight some Jem'Hadar at some point?)
Yes, I can totally see that in the future, people may live productive lives past the century mark, but I can't believe they would still be going on away missions, physically fighting, etc. My grandma is in great health for her 90+ years, and has a sharp mind, but I wouldn't necessarily have her serving as a foot soldier! I just wonder if, in his travels in the Intelligence field, Vaughn didn't have some sort of genetic enhancements done, or if he encountered an alien lifeform or anomaly that slowed his aging process (haha- does he have a Lazarus pool stored away somewhere, like Ra Al Ghul in the Batman comics?)