Yes, but that's a very stretched interpretation.
Sure, but then again, it's trying to explain away a nonsensically written Trek factoid.
The idea is that unless Kes has her first child at this short window of opportunity they call elogium, she won't be able to have any, ever. There is no equivalent to that in human biology, but that's neither here nor there. Kes' own description of elogium does not equate it with puberty - that's just Janeway jumping to conclusions.
The universal translator converts all systems of measurement to the listeners standard.
Well, seconds and minutes, certainly - they are something we can easily verify, as they are quoted in contexts where they tick away as we watch. But whether "year" is a system of measurement or a physical phenomenon in its own right is a somewhat different matter. It does have its independent astronomical definition, after all. And if the local year comes with seasons, it will probably greatly affect one's perception of one's age ("She's thirteen springs young"; "He has seen two hundred and fifty-three winters").
As for McCoy, he might have been stricken with a dozen space ailments that make him an atypical specimen. Picard was a decade younger than Patrick Stewart, but Bashir was the same age as Siddig El Fadil; perhaps humans in fact age more slowly during their productive middle years, and thus not merely live longer but also prosper longer? Mark Jameson did seem awfully displeased with being a somewhat typical 85-year-old, thinking nature had dealt him with atypically bad cards for the 24th century.