You can basically guarantee that you have under 18 people ERP in FFXIV, sex animations make it easier for people who have poor skill in writing as "They just want to watch FF porn" so probably easier for them to partake in it now, not that being under 18 makes you illiterate but its a safer bet to be able to categorise that way.
I don't quite understand why clubs advertise in the way they do now, anyone in the social side of FF will know that this is available anyways, good luck finding a club that DOESNT do something ERP related either directly by staff or indirectly by just the patrons.

At the end of the day your "age gateway" is payment, Second Life could be pointed to as free but you have to have a payment record on file to be able to enter Adult rated zones and its pretty easy to just bring up the marketplace for Second Life and see just what kind of thing is involved there.

I just don't like seeing the filth level advertisements in the game, it reminds me of what FF has become.