Or not... McCoy lived at least to the age of 147 (though he looked very old). Kevin Uxbridge (yes, he wasn't really Human, but he was pretending to be) and his wife (who was Human) were supposed to be 85, even though the actors were around 60. I also believe that the date of Picard's birth given in an episode, I think it's "Conundrum", makes him well over 60 in TNG, even though Stewart was in his late 40s when the show started. And, if we go by the books,Seems like humans are quite short living creature in comparison with Vulcans, Klingons (if they don't die in battle that is), Romulans, and now Cardassians...
If you take books under consideration, Dukat was waaaaay older that 55.
Nechayev must be at least 70 years old on TNG/DS9.