Mid-life crises are very common for people in their late 40's to early 50's, especially for woman. A woman by that age has been a wife and mother for a couple of decades for many. All her time was spent raising and caring for the children, but now they are out of the house or in their last years of HS, and they turn back to themselves. For the first time in maybe a couple of decades they can worry about themselves, do they still look attractive, are they still charming. Many go out and have an affair or divorce their spouse because they want something that has always bugged them and now is their chance to get it. I am sure she is thinking having a fling with a HS student shows that she is just as hot as that 18 year old, stupid but not in their mind. Its reliving the past that they may or may not have had, allowing them to feel good about where they are in life.