Dynamo wrote:There is plenty of documentation everywhere but how many people actually know this?

It's rather worse than that.
How many people are actually curious enough to question the status-quo? Or, brave enough to actually flaunt convention.
I like the shot of FDR in the Smithsonian article, but it's only one of a great many from that period showing youngsters so attired. Too, it seems that the age at which children began to wear "adult clothes" (which removed, permanently, the skirt option for guys) was variable and I've seen ranges between as low as 3 and as high as 7. Other examples of such rigs can be seen from various museum collections at
OMG That Dress (under "children's").
What the author of the article misses, however, is that as women gravitated toward more masculine (the author uses the term "neutral", which I would dispute in context) styles it had the effect of pushing the guys farther and farther into a corner that there's no escape from. Like "getting painted into a corner", there's no way out until either the paint dries or the frustrated individual either takes out a wall or decides to say, "Screw it" and walk out over the fresh paint (both of which are rather rash acts).
But, a male author could not write about such things without getting called "whiny" or worse, so the guys "man up" and just take it. And the internal pressure rises a bit more.