Nice topic.
I’m the same as you, mainly adults, but lots of teenagers too – 13 out of 31 actually! And the rest adults.
1. 8, but haven’t taught that young for a long time now. Would probably prefer 10 upwards, as this is what I’m used to and I can talk to them more like an adult from 10 onwards…!
2. I took on a 6 year old for a trial once and she cried. Clearly wasn’t ready and was pushed by the mum… which I’m very against… but hey, I might have just been really intimidating and she could now be with a teacher she doesn’t cry with…!! I also taught another 5 year old and 8 year old at the same time which really didn’t work. Obviously the older one was more focused than the other. But as they were brother and sister they kept distracting each other or messing around.
I’m not really a kids person and I find it far more straightforward to deal with fully formed humans that can keep still lol!