Thats a really huge question!
I've been teaching people of all ages for just over ten years and i have to say the older ones seem more interested to learn. I honestly believe this generation is becoming kinda lazy with everything just a click away for them i.e. 1,000 TV channels (I remember when there were only three) and computer games seem to be the distraction for most.
As teachers we can only encourage but once the student(s) are back home they can do whatever they wat to, and practicing an instrument for example seems hard work to them but pressing play on their xbox or ps3 is much easier and far more enjoyable IN THE SHORT TERM.
Going back a couple of decades and we would look forward to lessons and wanted to achieve more to become a better person but unfortunately it seems we cannot make them learn.
It is however always nice when a student does shine through and want to do well but they are few and far between.
Thats just my two cents :)