Mixed age groups work well for us too. But really it may take until high school or even college to find a true peer group that sticks. And maybe that is true for more than just GT kids? I kind of feel if my kids enjoy being social and continue building their social skills, I'm not going to stress about it too much. We are lucky that we have many MG+ kids in our area and a GT homeschooling co-op, that we don't get to see enough, but has been a good fit as well.