
I can't speak for anyone else, but to me it's not derogatory, it's a simple choice.
I wouldn't join a guild that wasn't 18+ personally, simply because I enjoy playing with people who are around the same point in life as I am. While I RP freely with everyone no matter their age (as long as they're decent RPers), I prefer to hang out with fellow adults OOC-ly, just as I prefer to hang out with fellow adults in RL.
As when I was a teenager, I preferred to hang out and RP and play with fellow teenagers. I think it's perfectly natural.
And yes, there's also the legal issues.
I wouldn't join a guild that wasn't 18+ personally, simply because I enjoy playing with people who are around the same point in life as I am. While I RP freely with everyone no matter their age (as long as they're decent RPers), I prefer to hang out with fellow adults OOC-ly, just as I prefer to hang out with fellow adults in RL.
As when I was a teenager, I preferred to hang out and RP and play with fellow teenagers. I think it's perfectly natural.
And yes, there's also the legal issues.