In a previous GR, we discussed the tricky way the point of view in JA's novels can slide back and forth between the factual Omniscient Narrator's and an individual character's, even though it looks like it's still the ON (or a particular character) speaking. Thanks for making me take a second look at the passage you quoted, because that's what I think happens here:

It sometimes happens, that a woman is handsomer at twenty-nine than she was ten years before; and, generally speaking, if there has been neither ill health nor anxiety, it is a time of life at which scarcely any charm is lost. It was so with Elizabeth, still the same handsome Miss Elliot that she had begun to be thirteen years ago; and Sir Walter might be excused, therefore, in forgetting her age, or, at least, be deemed only half a fool, for thinking himself and Elizabeth as blooming as ever,...

Up to this point, I think we have the ON stating facts, though after she mentions Sir Walter, the POV *gradually* begins to shift to Sir Walter's in mid-sentence!

...amidst the wreck of the good looks of every body else; for he could plainly see how old all the rest of his family and acquaintance were growing. Anne haggard, Mary coarse, every face in the neighbourhood worsting, and the rapid increase of crow's foot about Lady Russell's temples had long been a distress to him.