Like so many guys of a certain age on Zity, I grew up when communal showering in schools was normal / mandatory. So, what with PE / Games, Swimming, some school teams activities etc., etc.....you saw your peers (& sometimes older boys) naked quite frequently.
I think that there was a lot of discreet 'checking each other out' that went on. When we were younger, say 11 - 13, & many of use were prepubescent...I am sure it was just natural curiosity allied to a sort of juvenile 'male bonding'. Plus, I was a very slim boy & did not have a huge endowment. Has the 'penis envy' theory been discredited nowadays? I certainly used to admire ( as opposed to being pathologically jealous ) my more athletic, well -endowed friends.
Later, there was sometimes an atmosphere of charged sexuality when testosterone (& other teen hormones ( kicked in). Some boys were naturally shy, many seemed not to care, but others were definitely exhibitionists, almost flaunting themselves and 'daring' you to look. I am certain that this was much more to do with their perceived status as 'Alpha Males' on their part and not anything homosexual per se.
In fact...that was the unwritten law. No one could be seen, or thought, to be actually looking or staring intently / directly. In that world of boys...it was simply considered to be the worst crime you could commit. It was clearly the same in any country and any era. No one, but no one wanted to be labelled as 'Gay' or a 'Fag', 'Pouffe', 'Queer','Nancy Boy', 'Ponce' or whatever derogatory term boys habitually used.
Out of school, I did have a few friends who (like so many have mentioned) I had occasional penis / wanking fun....in that slot between puberty kicking in and then boys 'moving on' to girls soon afterwards. I guess it was all a rite of passage for so many of us & actually a pretty normal part of our nascent / developing sexual awareness etc. Most of my friends had bigger cocks than mine....but, ultimately, it never seemed to really matter to anyone (on reflection).