Yep it get irritating speaking English and getting answered in Japanese. I have threatened them, bribed them etc. But it just doesn't work.
The government started pushing English in Elementary school a few years ago but it is still not an "official" part of the curriculum. So there is no text or anything. I have to create all of my own lesson plans and it is a pain at times. I teach 1st grade to 6th grade and as you stated the older they get the less genki they are about studying English. But it is still class by class.
It is not too bad over all as I get all of the school holidays off which amounts to about 10 weeks a year.
I actually have only been to Tokyo once. I live in the Kansai area in Hyogo prefecture. I actually live on Awaji Island. Some of you may remember the big earthquake in 95 in Kobe. The epicenter was actually on Awaji. I moved here about 3 months after the quake.
Well, no reason to be in Tokyo, when you can be on Awaji. Nice place. I use to sneak on to the bullet train from Tokyo, all the way to Osaka, for free. (Don't think the scam works anymore, but it was nice then.)
I made it to Awaji only once. Anyway, all the best to you in Japan. I miss the sushi. Can't find good sushi here in Germany, at least where I am. Fake Vietnamese stuff. It must be great on the island there.