My understanding, from my own threads on the subject, is that it's a matter of preference.

That is, if you'd rather not have to invest as much (or any?) real money in BVE-ing reload gunners to hit the reload-caps for later-level DP guns, it is better to class later (more reload growth, plus lighter on the crew/weight-side).  If money is no object, and you'd rather just have useful DP guns on lower level ships, class at 62.  Classing at 62 will, however, require more vetting to hit the reload-caps later-on, and be heavier crew-wise.

Personally, I am levelling a number of BOs simultaneously (presently, one as a Mogami(1938) CL-escort, and another to be BB or CV-line); incrementally levelling elite reloads as armament sailors.  It it my "hope" that my elite reloads will make level 120 as armament sailors before any of my individual BOs reach a point where they "need" DP guns in their T-slots.  If not for getting my reloads (as armament sailors) that much further ahead of BOs, levelling several BOs has another advantage: credits (I am one level from Mogami with my escort BO, without nearly the funds to buy it.  Levelling other BOs through the same ships already in port, I hope, will solve this problem).

I'll go so far as to buy elites (actually prefer spendin' a few bucks for a sure-thing good crew, as opposed to spending what could be 'hours' rolling the dice for similar stats).  I don't BVE though but, then, at my still low-level there's not much of a point (would lose too many vets in battle). 

It is amazing how much some will invest in this game, though .. i've heard stories of "thousand-dollar" crews, etc. ... meanwhile, some will BVE even at blitz-level just to rape the newbz.  There's a certain Mandel skipper in blitz who tries to deny that all he does is super BVE an auto-aiming PCA (basically, akin to taking the beginner's/training Yamato into blitzkrieg).  Yet never seems able to disprove the allegation by simultaneously firing, without turning, his guns in opposite directions (there's a tendency for auto-aim guidelines to cross if you invert your aim while turning, and some auto-aimers use shooting at this moment to 'prove' that they're using manual).

so 120 is good?

class them at level one hundred.....enter world at war.....watch them spam away...gg