It's difficult, basically I'd tell them to mind their own business, that's the easiest way out!
Now if you fell the need to know what is going on, imagine it like this:
It's an individually weighted a+b+c+d version with a good chance of e happening.
What does that mean: It's basically a clothing optional beach resort with a swinger club (swing as in lifestyle!!) attached, with single men allowed to attend.
Now if the boy is really gay, he'll probably have not much fun, usually gay contact are pretty much "outlawed" in these places. It makes things easier for him, if he doesn't mind working on a lady with other guys doing the same...if you know what I mean...
If he likes to go for girls, well, it depends what sort of girl he fancies: The young and pretty ones...forget it!
The older and sexually highly active ones...these are ones attending for sure.
As far as age is concerned, he'll be one if the youngest for sure.
One thing I cannot comment on: I hear there are increasingly bunches of people mainly from the USA attending, that see the whole thing more in spring break tradition, that is, drinking like crazy, party all the time, but in general not running around naked but always interested in watching such activity. If this is true, then a lot of sexual fun is replaced by a lot of Daytona Beach sort of fun.
In general: Wait until he returns and tell us every word he says.
And calm down his mother...there are condoms everywhere, hopefully he knows how to use them...