This is going to be an unsatisfactory answer, but: it depends. We generally play with our rates a little using good old supply and demand. If I'm swamped with appointments (usually in the summer), I experiment with raising my rates until my scheduling is more reasonable.
Experience can be an increase, especially if an escort has tons of good reviews.
Age can decrease rates, although not generally until 35ish or so. Then again, most over-35 escorts lie about their age, but it's kind of an open secret.