My Little Pony 2F: Ponibooru, We Hardly Knew Ye...

[thubby]

Uh, what?

one of the best fan fictions ever
and luna works exactly like you described.

Life= millennia+
Age difference = decade, maybe

Luna also has an established implicit power increase above Celestia's own. So.

fanon aside, the royal sisters really don't act like immortals you'd see in other media, and it's really irrelevant who's stronger now. but you're missing the point.

im not saying luna can't be the stronger more protective one, just that people give celestia that role because it correlates to a cery real and normal occurrence.