I had a longer post that was swallowed by my browser-
In any case, 60 is the new 40. It simply is- if you look at pictures through the generations you can see the difference. From the 1960s forward, people simply could and did take better care of themselves.
And, youth is more highly prized, so there are so many more attempts at appearing as young as possible than there ever was. Teen culture wasn't even a thing until almost the 50s (Bing Crosby was practically some upstart kid when be started out).
It's amazing that Robert Vaughan was only three years older than David McCallum. Perfect example! At 32 years old at the start of U.N.C.L.E., his "bearing" was certainly on the mature side. He was a serious, responsible, seasoned pro. At 32 years old today (and recent remake of U.N.C.L.E. aside), you're more likely to play a high school senior or the cocky newbie breaking all the rules, but getting the job done with the help of a deux ex machina!
Similarly, Roger Moore is older than Connery. You would have thought he was 10 years younger.