Yes, the curse pretty much broke now. Her age was based upon how she felt about herself. If she felt too self concious, she became old, if she felt good about herself, or she was caring about something else, she became young.
About the gray hair, it's more of a symbolic thing than anything. I bet it has to do with the fact that she's more grown up inside. Before she was cursed, before she met Howl, she lived a pretty dull life, and she thought she wasn't pretty at all. She also tended to the hat shop, even though it wasn't what she really wanted to do. But after her experiece with the curse and Howl, she now is more daring to do things she wants to, and Howl made her feel less self-concious. It shows she's grown up.
that's what it is in my point of veiw. However, Hayao Miyazaki probably left this unexplained to make us think, and there are MANY different opinons on why these things happened.
