I am a native speaker, I was born and lived in England until I got married in Poland (more years ago than I like to think), my father was Polish, my mother English but although we belonged to the Polish community we did not speak Polish at home. My Polish is good, but not perfect which makes it easier for me to understand the stress of speaking a second language.
I have spent 30 years teaching individually, and in state schools. I don' tthnk there is an age group I have not ticked off, but it would be difficult to say which age group I prefer. It has been said that 'a day on which you don't learn anything is a day wasted', I totally agree with this, and it is true for me too. It is amazing how much I have learnt from my various pupils.