Why are Alphinaud and Alisaie rather short for Elezen?

[Belhi]

I wouldn't mind if they aged them as time goes by. It already seems odd to me that someone as young as Alphinaud is taken so seriously in the story (leading a company, negotiating with world leaders) if he got an older appearance I think it would make it more believable for me.

If you think of societies in the setting we are talking about and the fact that Alphinaud is basically part of an influential and rich Shalayan family, is social status makes up for his age. Alphinaud's family supplies a good portion of the Scion's finances. His words hold clout because his family holds clout.

He is a young noble basically and acts much like a young noble would. He assumes power and authority because it was the world he was raised into. Arrogent yes, but his heart is in the right place. Remember he did help that young refugee girl find her parents back in 2.3 and he is usually pretty respectful of people.

I mean, do people really want a humble Alphinaud? The would seem pretty weird to me.