Viera males should be smaller like Au Ra females

[Agaziel]

Considering that it takes 13 years to barely find out something is a male is pretty ridiculous. Also the fact that Male Vieras retain a Youthful look for over 200 years that's "nigh impossible to discern one's age from outward appearances". I don't see a problem with a male looking similar to Fran or any other female Viera we've seen. Of course they wouldn't have a bust or as many curves but facial wise they'd still be young looking like Fran. Fran must be really old considering how mad she was at Vaan talking about her age in FF12 all the way into FF14 where she doesn't even look like she aged.

Even so I can't imagine them being with teenager faces much less too much slim so sorry not even with your lore explanations I can't figure them out the way you describe,
I imagine them much more like tall due to adaptation to reach the highest provisions and spots in the forest and with adult faces shaped by the exposure of the weather changes and athletic bodies where you see the muscular mass due to adapt a life in the forest where they have to be agile enough to run from other beasts that want to eat their faces or they need strength to hunt for surviving and the use of intelligence for protection of their tribe.
We talking about a forest with tall trees.