My answer: by George McNerlin, Central Baptist, Chattanooga, TN
Our solution was to overlap. We now have a college and career group, 18-25...a 20-35 class...a 30-45 class...and a 40+ class. (those who are 60+ usually prefer our seniors ministry). We later added a single parents class, (that's going like gang busters), and are about to add a special needs class, "Boundaries", and a women only class. We are not legalistic about the age thing, if within reason, however, I will not allow a man over 30 into the college and career class.
The main dividing line seems to be about 35. Our 20 something's often complain if we do joint activities with the whole group. You really have to watch out for the younger women. We have a couple of guys in their 30's who, though not "predators", still make the younger ladies very uncomfortable. They have no people skills and we constantly have toteach them those skills. One, slightly challenged man, has been asked not to hug women, period, because of his lack of discretion. However, I have much more patience with the "simple" than I do with predators.