[Elladan and Elrohir]

I am in total favor of the baby boom theory; in fact, I've held it for a long time while not calling it by that name. After all, as others have pointed out, Gondor had many allies and few enemies after WotR, and duh, Sauron's gone, which certainly helps.

I think there is evidence of this in the book. After all, it says something along the lines of, Minas Tirith became greater and more beautiful than it had ever been, even in the days of Elendil. So obviously there must have been a boom of some kind. Probably, a grace period granted by the Valar, an echo of Numenor in the Second Age.