Randomly perusing wiki I ran across this tidbit, subtly suggesting the similarity of degree of this specific cultural history of the two, and never having heard of same on remotely that scale regarding Japan am now wondering if it has been actually academically shown to be similar, do they actually compare? Not that there is anything wrong with it.*
*Seinfeld reference. Why the fuck doesn’t the /SIZE thing work anymore?
Yes. Google/wiki the words “nanshoku” and “shudo”.
Heh, wow.
An FYI, the link goes directly to the wiki entry on Anal Sex - probably NSFW, so I reported the post to have it broken (no offense mean, OR) There are probably not too many people who’re going to read a thread on Japanese / Greek pederasty at work on a Sunday anyway
And now I’m off to google 
In both cases it was typically an older male who took on a younger male to teach how to be a man, particularly how to fight. Men weren’t required to have sex with the boys or anything like that, but master/tutor love was highly romanticized in both cultures and sexual relationships were not frowned upon and even in some cases encouraged.
Both cultures allowed the relationships to continue after the boy reached manhood, but the Japanese were a bit more open to adult male/male relationships. There were accounts I’ve read of lovers where the “boy” was actually older than his “mentor” and both of them continued their relationship until their deaths in their 70s or 80s. I also read more accounts of Japanese lovers who never married women but I know such Greek men also existed and also could be highly honored.
There are other cultures which have this relationship with men and younger boys. In Papa New Guinea, the boys were required to have sex with the men before they became adults. Gay historians usually divide gay relationships in cultures into three types: Man/boy, man/man-as-woman, and egalitarian. A culture could have any or all the of the three types. Man/boy involves an older man with a younger boy, man as woman was where one of the partners was considered to be like a woman or a woman (still seen today among some central American cultures), and egalitarian is, of course, where both partners are adults and regarded as two fully functional men. The man/boy relationship is very common and can be found all over the world.