Intelligence, goodness, humanity, excitement, serenity. Over time, these are the things that change the musculature of your face, as do laughter, and animation, and especially whatever peace you can broker with the person inside. It's furrow, pinch, and judgement that make us look older - our mothers were right. They said that if you made certain faces, they would stick, and they do. But our mothers forgot that faces of kindness and integrity stick as well.
"Grace (Eventually): Thoughts on Faith". Book by Anne Lamott, 2007.