i agree, it all depends.

as far as different age relationships, for some reason i seem to recall seeing more instances of older guys with younger women, but that's just my own experience. overall, i think most people tend to stick to around the same age.

on the other hand, my girlfriend is almost 7 years older than i am..her parents frowned upon us at first, but that could've also been because i am an American, former military AND younger.

age is relative. there are plenty of mature thinking 20 year olds and just as many immature 30 and 40 year olds..

however, i also agree that it seems like doing anything too out of the ordinary puts Japanese at risk of losing face, and that MAY be one reason to date/marry in the same age range, but this topic is something i'll have to ask more people about after my move.

thanks for bringing this subject up.