Enjo Kosai is a general term.
Enjo Kosai is a general term, it's doubtful that many (most?) that do it thinks of sexual intercourse when they do it, to some it's just a way of pleasing people (and maybe also yourself) and getting some extra cash.
As for kogyaru's attitudes.
Well... That's girls, it's actually not limited to Japan, nor any particular time era.
Though it should be noted that girls that gone unsupervised could lead to negative situations.
As for socialization with compensation.
Er... This is an age old thing, and I don't mean sex for money.
One of the oldest example is marriage. One of the most recent ones is dating. It's not strange at all though should a girl proposed to go on a date in exchange of her protection, or perharps just to have fun.
"Jaa nee... Deeto ikkai!" ("Well then... One date!")
Okay, be honest, how many Gils did you spent on the date or to get the date?
As for sexual intercourse for money.
Well... Marriage is also a kind of way is a sexual intercourse for money or any other type of compensation, provided there's a sexual intercourse in thr marriage.
Now for girls having sexual intercourse in exchange for money or other type of compensation.
I think that the question that should be ask is... has the permission already been given for a sexual intercourse?
If the girl is an orphan without any guardian, then... I guess that's really up for her to do things according to what she wants.
But if the girl has a parent or a guardian, then... what's her parent or guardian say regarding this matter? Like someone once said, the parent or guardian don't care how old she really, what they want is, has she been given permission by them to do so?
As for having sexual intercourse with young girls.
It should be noted that teenage girls are actually adults. And the last few thousands years, that is what it always been, only recently that their status as adults were dropped and they're reduced as mere children until the age of 18 years old (or even 21 years old?). As matter in fact, the term 'teenager' is only a term that was used recently.
Of course, by the time they're 18 years old, they're pretty quite old. So I guess you see the reason on why men actually prefered teenage girls than... ahem, 'older girls'.