I would say age definitely is a factor. I can't say for certain, since SE hasn't done a census, but I think it's a safe bet to assume the most common average player age in XIV is somewhere between 20-35. Older players tend to be more patient and tend to be more mature (i.e. they're more likely to mentor a new player, than trashtalk them about how much they suck.) Also with age, people tend to think before they speak, (assuming of course they aren't exhausted or drunk) wheras youger players tend to mouth off.

As for the relative quiet, I'm guessing that most people tend to either use VOIP, or chat within thier own linkshell, I know the one I belong to uses both. New players that don't have one are as you said are invited into LS pretty quick.