I'm in my 60's and look about 80 with short hair! I have it just touching my shoulders and wear it up,sometimes, too. It is such an individual thing. My best friend, same age, had hers cut from long to a gamine, Mia Farrow style a couple of years ago and it took years off her.
There are so many factors, face shape, neck length, forehead width, shape of eyes that can influence how you look so I would never make pronouncements about how one should wear one's hair, according to age.
As Julia herself has made a point of discussing her hair, I certainly feel that we are at liberty to discuss it too......