As humans posessing an intellect, we are all judgmental, whether it is in regard to people, the the places we go, things we eat, etc, etc. One can call it steroetyping, but as humans we learn from experience, and then make decisions based on the lessons we've learned and the clues that we pick up. So, when a mature woman prefers to be with older, mature men, and says so based on experience, more than likely she has picked up on certain clues that are telling her that this situation may bear some resemblance to other, similar situations. Not exactly the same, as no two people are the same, but enough that her radar is up.
By way of example, my wife and I, both 40 year old, have an open marriage. She tends to, though it is not a hard and fast rule, prefer guys in their 30's on up, and preferably married. It has been her experience that younger guys tend to look at her and try to treat her as their "pussy on demand". There have been younger guys that she has played with that have tried to get her to ditch work, ditch doctor's appointments, ditch family obligations, drive to them in bad weather, and disrespected our marriage because they wanted to blow a load at that given moment in time, and they didn't give a ******* who it inconvenienced. The older guys that she has played with, especially the married ones, realize that slipping away for a nooner isn't always that simple because they too have responsibilities, time commitments, and family commitments that you can't just flippantly disregard just to have sex. Not that a younger guy doesn't or can't understand that, but that the chances of that happening with more mature men is less likely to happen.