Basically, it's your choice. But like everyone else has said, please weigh the value of being in Playboy against the dignity, class, and respect you and your GLO currently possess. Like it or not, your posing will likely negatively affect people's perceptions of you as well as the women you call your sisters.
I kinda feel like it's like getting a tattoo. So many college freshmen go out and do it, just because they can (not around Mom and Dad anymore, just let off the leash, etc). They end up getting something retarded and for the rest of their lives they're that kid with Marvin the Martian smoking a blunt between their shoulder blades.
Playboy will still be accepting pictures in 2 years. Wait until you've graduated and begun to establish a life outside college. If you still want to do it then, you'll know that you wnt to do it for real, for you personally.
Playboy isn't going anywhere.
And this is my own personal opinion, but what if a member of your family who didn't know you were posing happened to pick up that issue? I for one stumbled across my GRANDFATHER'S cache of porn when I was 11... that forever ruled out any chance of EVER choosing that lifestyle. Him opening a magazine, seeing his granddaughter.... ewwwwwwwwwwwwww.