If they are talking about a new show, in 2390-ish, in the style of TNG, with guest appearances from Bermantrek characters but a mostly new cast, I'm in. If they want to make the Simpsons parody of a TOS movie a reality and do a Geriatrek, no way.
Well, this is the future. Life expectancy in the 24th (almost 25th!) century is, what, 110? 120? Assume McCoy's comment about being 137 and "not havin' died" suggests that it's not much higher.
Anyway, actors who are in their 60s and 70s are mid-life characters in series. There's no reason to impose our societal constraints on them. As long as the writers play this up and make us believe it's not a problem, there's no reason it wouldn't fly.