Bethberry, your post is fascinating, and you make some good points - and everyone has their own image of the characters. I suppose I have a bias for Blanchett because the first time I saw her she was playing Elizabeth I and I thought her a younger Glenda Jackson. She is obviously not 7000 years old, but in my opinion, she is in her prime, old enough to play the role with maturity and dignity. I am old enough to remember when Judi Dench was young and beautiful and she too has played Elizabeth I with grace and dignity. However, I wouldn't give her the role of Galadriel now! Would you?
It could be a lot worse. Did you know that Kylie Minogue applied for the role? I kid you not! Fortunately, PJ told her kindly that she was too short for an Elf. Short, yeah.
For what it's worth, a friend of mine decribed CB as a kind of Elle McPherson, which I thought rude of her, but hey, she's entitled!
Personally, I think Elves age or don't age according to what Tolkien wanted to say at the time he was creating a character.