Yeah, the post is ignoring the fact the reason someone would lie isn't because of that, but because Toph is a fragile looking, petite little, blind girl.

Age isn't the reason, body shape is the reason. Katara don't looks like an anorexic. And by what we've seen of Ozai and Bumi, the more powerful the bender is, he tends to have more muscle.

And Aang being the avatar and all, they couldn't lie about how he looked.