The discussion on the diversity of a school is interesting because the judo dojo i go to is pretty much all VERY high level black belts. The average age is 45-50 with 10-30 years of martial arts experience, so there is a huge wealth of knowledge. Im 17 and I fit it in excellently, because if i ever do something wrong it will get corrected very quickly. I've been doing martial arts formally for 4 years and my dad has run a Tai Chi Chuan school for longer than i've been alive. It's weird thinking that older more knowledgeable martial artist could be intimidating. I've just never seen them that way probably because of my background. I do agree that mixed classes are the best though. My teacher has started trusting me teaching some of the few lesser experienced people that come to our class. It's a very rewarding and beneficial experience breaking down the moves, not only for them, but for myself.