Not a CFer here, but from one woman to another..... if they EVER want kids, I would seriously recommend against it. Granted, I had 3 little ones growing in there but I know so many women who regret it after having children. I took mine out 4 years ago, and still have this HUGE scar from my stomach stretching. I have friends/coworkers who've had the same problem and just had one baby. Just a coinsideration.
I got mine done at 16, my mom actually took me. It was great, but if I had to do it over again, thinking a little into the future and KNOWING I wanted kids someday.... I would NOT have done it.
As far as it being pierced and CF is concerned, I can't imainge it would be a problem. No different really than having peirced ears. Mark has his tongue pierced and has for about 10 years now, with no problems whatsoever. I'd say as long as they are taking care of it, cleaning it, wearing good quality rings, it should not be a problem.