Headless Horse wrote:True, but in the absence of any dialogue explicitly laying out that ponies live for hundreds of years, I'm chalking that up to poorly thought out writing that tried to mash up WWU and FAD a little too carelessly.

There's equally no reason for their life spans
not to differ from humans, though. It's not necessary that lives default to the human standard. It's an easy excuse to make, at least.
Besides, I don't think they talk about age much. Just the same as how politics, relations with foreign cultures, and set-rules for the magic system aren't really issues, neither is age. They'll tell that part of the story when they get there, otherwise the only thing that matters is "baby, young, mature, old, timeless"