@mathprofbrony
 
There is actually a pic here on Derpibooru that depicts Principal Celestia and Vice-Principal Luna as at least middle-aged.

@mathprofbrony  
Pretty much this!

Think about what age you would be if you could be any age you wanted, and had been.
 
Old men get respect. Old men get called “sir.” If you’re pretty much over the dating thing, and have no actual physical worries about a frail body and just get the social value of it, being old is the pips.
 
For a guy.
 
For women? Sheesh. Women have to be eternally young and beautiful. We’re supposed to respect old women, but take a glance around any society and see how we treat widows or spinsters compared to men of the same age. Not cool.
 
So I’m betting 7nights didn’t really think about this when picking their forms; Celestia and Luna were young because immortal females who can be any age will be the most useful apparent age to be (Luna slightly younger, this being canon) and immortal males will do the same.
 
A humanized Celestia choosing to manifest as an elderly but still iron-jawed matron could be awesome. Somebody draw it. Maybe Celestia in three forms as Maiden, Mother and Crone.

Luna, you are questioning the form a shapeshifter takes. He looks like whatever he wants to be, so don’t question it unless you want to go insane. Yet again.

Because he’s not supposed to make se- oh @Klonoahedgehog damnit…

What fun is there in making sense?