That's the point of the film, I think.
I think I agree. Wasn't Harve Bennett's idea to go this route, to make the characters match more believably to the age of the actors?
I think that was brilliant! And McCoy is my favourite character in TOS, mostly due to DeForest Kelley's excellent acting skills.
Karl Urban is doing a great job of carrying the torch, even if he looks far too young for it.