[MMM]

I think a note might be a little embarrassing. If it really is an older guy, he might not hear so good... and then you might be in a bit of a hard spot. The landlord telling you "you are the only young guy living here" might be a subtle hint to "you might need to deal with some oldster stuff".

I would recommend a present an older man might like (maybe a bottle of sake) and laying down the hint that you go to bed at XX hour.

Maybe I am totally off, but this is the safest route to go. Certainly some Japanese would appreciate the direct information, but without knowing for sure...